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A Dictionary of Measures, Units and Conversions
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A Dictionary of Units
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The Systeme International [S I]
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Le Systeme international d'Unites officially came into being in October 1960
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and has been adopted by nearly all countries, though the amount of actual usage
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varies considerably.
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It is based upon 7 principal units, 1 in each of 7 different categories -
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Category Name Abbreviation
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Length metre m
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Mass kilogram kg
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Time second s
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Electric current ampere A
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Temperature kelvin K
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Amount of substance mole mol
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Luminous intensity candela cd
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Definitions of these basic units are given.
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Each of these units may take a prefix.
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From these basic units many other units are derived and named.
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Definitions of the Seven Basic S I Units
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metre [m]
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The metre is the basic unit of length. It is the distance light
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travels, in a vacuum, in 1/299792458th of a second.
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kilogram [kg]
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The kilogram is the basic unit of mass. It is the mass of an
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international prototype in the form of a platinum-iridium cylinder kept
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at Sevres in France. It is now the only basic unit still defined in
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terms of a material object, and also the only one with a prefix[kilo]
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already in place.
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second [s]
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The second is the basic unit of time. It is the length of time taken
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for 9192631770 periods of vibration of the caesium-133 atom to occur.
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ampere [A]
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The ampere is the basic unit of electric current. It is that current
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which produces a specified force between two parallel wires which are 1
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metre apart in a vacuum.It is named after the French physicist Andre
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Ampere (1775-1836).
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kelvin [K]
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The kelvin is the basic unit of temperature. It is 1/273.16th of the
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thermodynamic temperature of the triple point of water. It is named
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after the Scottish mathematician and physicist William Thomson 1st Lord
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Kelvin (1824-1907).
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mole [mol]
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The mole is the basic unit of substance. It is the amount of substance
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that contains as many elementary units as there are atoms in 0.012 kg
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of carbon-12.
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candela [cd]
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The candela is the basic unit of luminous intensity. It is the
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intensity of a source of light of a specified frequency, which gives a
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specified amount of power in a given direction.
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Derived Units of the S I
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From the 7 basic units of the SI many other units are derived for a variety of
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purposes. Only some of them are explained here. The units printed in bold are
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either basic units or else, in some cases, are themselves derived.
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farad [F]
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The farad is the SI unit of the capacitance of an electrical system,
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that is, its capacity to store electricity. It is a rather large unit
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as defined and is more often used as a microfarad. It is named after
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the English chemist and physicist Michael Faraday (1791-1867).
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hertz [Hz]
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The hertz is the SI unit of the frequency of a periodic phenomenon. One
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hertz indicates that 1 cycle of the phenomenon occurs every second. For
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most work much higher frequencies are needed such as the kiloherz [kHz]
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and megaherz [MHz]. It is named after the German physicist Heinrich
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Rudolph Herz (1857-94).
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joule [J]
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The joule is the SI unit of work or energy. One joule is the amount of
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work done when an applied force of 1 newton moves through a distance of
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1 metre in the direction of the force.It is named after the English
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physicist James Prescott Joule (1818-89).
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newton [N]
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The newton is the SI unit of force. One newton is the force required to
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give a mass of 1 kilogram an acceleration of 1 metre per second per
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second. It is named after the English mathematician and physicist Sir
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Isaac Newton (1642-1727).
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ohm [*]
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The ohm is the SI unit of resistance of an electrical conductor. Its
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symbol, shown here as [*] is the Greek letter known as 'omega'. It is
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named after the German physicist Georg Simon Ohm (1789-1854).
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pascal [Pa]
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The pascal is the SI unit of pressure. One pascal is the pressure
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generated by a force of 1 newton acting on an area of 1 square metre.
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It is a rather small unit as defined and is more often used as a
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kilopascal [kPa]. It is named after the French mathematician, physicist
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and philosopher Blaise Pascal (1623-62).
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volt [V]
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The volt is the SI unit of electric potential. One volt is the
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difference of potential between two points of an electical conductor
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when a current of 1 ampere flowing between those points dissipates a
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power of 1 watt. It is named after the Italian physicist Count
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Alessandro Giuseppe Anastasio Volta (1745-1827).
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watt [W]
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The watt is used to measure power or the rate of doing work. One watt
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is a power of 1 joule per second. It is named after the Scottish
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engineer James Watt (1736-1819).
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Note that prefixes may be used in conjunction with any of the above units.
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The Prefixes of the S I
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The S I allows the sizes of units to be made bigger or smaller by the use of
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appropriate prefixes. For example, the electrical unit of a watt is not a big
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unit even in terms of ordinary household use, so it is generally used in terms
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of 1000 watts at a time. The prefix for 1000 is kilo so we use kilowatts[kW] as
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our unit of measurement. For makers of electricity, or bigger users such as
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industry, it is common to use megawatts[MW] or even gigawatts[GW]. The full
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range of prefixes with their [symbols or abbreviations] and their multiplying
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factors which are also given in other forms is
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yotta [Y] 1 000 000 000 000 000 000 000 000 = 10^24
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zetta [Z] 1 000 000 000 000 000 000 000 = 10^21
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exa [E] 1 000 000 000 000 000 000 = 10^18
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peta [P] 1 000 000 000 000 000 = 10^15
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tera [T] 1 000 000 000 000 = 10^12
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giga [G] 1 000 000 000 (a thousand millions = a billion)
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mega [M] 1 000 000 (a million)
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kilo [k] 1 000 (a thousand)
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hecto [h] 100
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deca [da]10
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1
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deci [d] 0.1
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centi [c] 0.01
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milli [m] 0.001 (a thousandth)
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micro [u] 0.000 001 (a millionth)
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nano [n] 0.000 000 001 (a thousand millionth)
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pico [p] 0.000 000 000 001 = 10^-12
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femto [f] 0.000 000 000 000 001 = 10^-15
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atto [a] 0.000 000 000 000 000 001 = 10^-18
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zepto [z] 0.000 000 000 000 000 000 001 = 10^-21
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yocto [y] 0.000 000 000 000 000 000 000 001 = 10^-24
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[u] the symbol used for micro is the Greek letter known as 'mu'
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Nearly all of the S I prefixes are multiples or sub-multiples of 1000. However,
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these are inconvenient for many purposes and so hecto, deca, deci, and centi
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are also used.
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deca also appears as deka [da] or [dk] in the USA and Contintental Europe. So
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much for standards!
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Conventions of Usage in the S I
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There are various rules laid down for the use of the SI and its units as well
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as some observations to be made that will help in its correct use.
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Any unit may take only ONE prefix. For example 'millimillimetre' is
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incorrect and should be written as 'micrometre'.
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Most prefixes which make a unit bigger are written in capital letters
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(M G T etc.), but when they make a unit smaller then lower case (m n p
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etc.) is used. Exceptions to this are the kilo [k] to avoid any
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possible confusion with kelvin [K]; hecto [h]; and deca [da] or [dk]
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A unit which is named after a person is written all in lower case
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(newton, volt, pascal etc.) when named in full, but starting with a
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capital letter (N V Pa etc.) when abbreviated. An exception to this
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rule is the litre which, if written as a lower case 'l' could be
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mistaken for a '1' (one) and so a capital 'L' is allowed as an
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alternative. It is intended that a single letter will be decided upon
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some time in the future when it becomes clear which letter is being
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favoured most in use.
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Units written in abbreviated form are NEVER pluralised. So 'm' could
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always be either 'metre' or 'metres'. 'ms' could represent 'metre
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second' (whatever that is) or, more correctly, 'millisecond'.
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An abbreviation (such as J N g Pa etc.) is NEVER followed by a
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full-stop unless it is the end of a sentence.
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To make numbers easier to read they may be divided into groups of 3
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separated by spaces (or half-spaces) but NOT commas.
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The SI preferred way of showing a decimal fraction is to use a comma
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(123,456) to separate the whole number from its fractional part. The
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practice of using a point, as is common in English-speaking countries,
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is acceptable providing only that the point is placed ON the line of
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the bottom edge of the numbers (123.456).
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It will be noted that many units are eponymous, that is they are named
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after persons. This is always someone who was prominent in the early
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work done within the field in which the unit is used.
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A Brief History of Measurement
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One of the earliest types of measurement concerned that of length. These
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measurements were usually based on parts of the body. A well documented example
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(the first) is the Egyptian cubit which was derived from the length of the arm
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from the elbow to the outstretched finger tips. By 2500 BC this had been
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standardised in a royal master cubit made of black marble (about 52 cm). This
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cubit was divided into 28 digits (roughly a finger width) which could be
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further divided into fractional parts, the smallest of these being only just
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over a millimetre.
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In England units of measurement were not properly standardised until the 13th
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century, though variations (and abuses) continued until long after that. For
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example, there were three different gallons (ale, wine and corn) up until 1824
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when the gallon was standardised.
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In the U S A the system of weights and measured first adopted was that of the
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English, though a few differences came in when decisions were made at the time
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of standardisation in 1836. For instance, the wine-gallon of 231 cubic inches
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was used instead of the English one (as defined in 1824) of about 277 cubic
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inches. The U S A also took as their standard of dry measure the old Winchester
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bushel of 2150.42 cubic inches, which gave a dry gallon of nearly 269 cubic
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inches.
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Even as late as the middle of the 20th century there were some differences in
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UK and US measures which were nominally the same. The UK inch measured 2.53998
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cm while the US inch was 2.540005 cm. Both were standardised at 2.54 cm in July
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1959, though the U S continued to use 'their' value for several years in land
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surveying work - this too is slowly being metricated.
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In France the metric system officially started in June 1799 with the declared
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intent of being 'For all people, for all time'. The unit of length was the
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metre which was defined as being one ten-millionth part of a quarter of the
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earth's circumference. The production of this standard required a very careful
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survey to be done which took several years. However, as more accurate
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instruments became available so the 'exactness' of the standard was called into
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question. Later efforts were directed at finding some absolute standard based
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on an observable physical phenomenon. Over two centuries this developed into
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the S I. So maybe their original slogan was more correct than anyone could have
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foreseen then.
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Metric System of Measurements
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Length Area
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10 millimetres = 1 centimetre 100 sq. mm = 1 sq. cm
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10 centimetres = 1 decimeter 10 000 sq. cm = 1 sq. metre
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10 decimetres = 1 metre 100 sq. metres = 1 are
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10 metres = 1 decametre 100 ares = 1 hectare
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10 decametres = 1 hectometre 10 000 sq. metres = 1 hectare
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10 hectometres = 1 kilometre 100 hectares = 1 sq. kilometre
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1000 metres = 1 kilometre 1 000 000 sq. metres = 1 sq. kilometre
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Volume Capacity
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1000 cu. mm = 1 cu. cm 10 millilitres = 1 centilitre
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1000 cu. cm = 1 cu. decimetre 10 centilitree = 1 decilitre
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1000 cu. dm = 1 cu. metre 10 decilitres = 1 litre
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1 million cu. cm = 1 cu. metre 1000 litres = 1 cu. metre
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Mass
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1000 grams = 1 kilogram
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1000 kilograms = 1 tonne
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The distinction between 'Volume' and 'Capacity' is artificial and kept here
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only for historic reasons.
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A millitre is a cubic centimetre and a cubic decimetre is a litre. But see
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under 'Volume' for problems with the litre.
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The U K (Imperial) System of Measurements
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Length Area
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12 inches = 1 foot 144 sq. inches = 1 square foot
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3 feet = 1 yard 9 sq. feet = 1 square yard
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22 yards = 1 chain 4840 sq. yards = 1 acre
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10 chains = 1 furlong 640 acres = 1 square mile
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8 furlongs = 1 mile
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5280 feet = 1 mile
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1760 yards = 1 mile Capacity
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20 fluid ounces = 1 pint
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Volume 4 gills = 1 pint
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1728 cu. inches = 1 cubic foot 2 pints = 1 quart
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27 cu. feet = 1 cubic yard 4 quarts = 1 gallon (8 pints)
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Mass (Avoirdupois)
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437.5 grains = 1 ounce Troy Weights
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16 ounces = 1 pound (7000 grains) 24 grains = 1 pennyweight
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14 pounds = 1 stone 20 pennyweights = 1 ounce (480 grains)
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8 stones = 1 hundredweight [cwt] 12 ounces = 1 pound (5760 grains)
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20 cwt = 1 ton (2240 pounds)
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Apothecaries' Measures Apothecaries' Weights
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20 minims = 1 fl.scruple 20 grains = 1 scruple
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3 fl.scruples = 1 fl.drachm 3 scruples = 1 drachm
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8 fl.drachms = 1 fl.ounce 8 drachms = 1 ounce (480 grains)
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20 fl.ounces = 1 pint 12 ounces = 1 pound (5760 grains)
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The old Imperial (now UK) system was originally defined by three standard
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measures - the yard, the pound and the gallon which were held in London. They
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are now defined by reference to the S I measures of the metre, the kilogram and
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the litre. These equivalent measures are exact.
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1 yard = 0.9144 metres - same as US
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1 pound = 0.453 592 37 kilograms - same as US
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1 gallon = 4.546 09 litres
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Note particularly that the UK gallon is a different size to the US gallon so
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that NO liquid measures of the same name are the same size in the UK and US
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systems.
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Also that the ton(UK) is 2240 pounds while a ton(US) is 2000 pounds. These are
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also referred to as a long ton and short ton respectively.
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--------------------------------------------------------------------------------
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Metrication in the U K
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There have been three major Weights and Measures Acts in recent times (1963,
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1976 and 1985) all gradually abolishing various units, as well re-defining the
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standards. All the Apothecaries' measures are gone, and of the Troy measures,
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only the ounce remains. Currently legislation has decreed that -
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From the 1st October 1995, for economic, public health, public safety and
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administrative purposes, only metric units are allowed EXCEPT that -
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* pounds and ounces for weighing of goods sold from bulk
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* pints and fluid ounces for beer, cider, waters, lemonades and fruit juices
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in RETURNABLE containers
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* therms for gas supply
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* fathoms for marine navigation
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may be used until 31st December 1999.
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The following may continue to be used WITHOUT time limit -
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* miles, yards, feet and inches for road traffic signs and related
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measurements of speed and distance
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* pints for dispensing draught beer and cider, and for milk in RETURNABLE
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containers
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* acres for land registration purposes
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* troy ounces for transactions in precious metals.
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Sports are exempt from all of this, but most of them have (voluntarily) changed
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their relevant regulations into statements of equivalent metric measures.
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That is how the legislation is framed. In common usage the 'old' units are
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still very apparent.
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--------------------------------------------------------------------------------
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The U S System of Measurements
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Most of the US system of measurements is the same as that for the UK. The
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biggest differences to be noted are in Capacity which has both liquid and dry
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measures as well as being based on a different standard - the US liquid gallon
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is smaller than the UK gallon. There is also a measurement known at the US
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survey foot. It is gradually being phased out as the maps and land plans are
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re-drawn under metrication. (The changeover is being made by putting 39.37 US
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survey feet = 12 metres)
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Length Area
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12 inches = 1 foot 144 sq. inches = 1 square foot
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3 feet = 1 yard 9 sq. feet = 1 square yard
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220 yards = 1 furlong 4840 sq. yards = 1 acre
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8 furlongs = 1 mile 640 acres = 1 square mile
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5280 feet = 1 mile 1 sq.mile = 1 section
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1760 yards = 1 mile 36 sections = 1 township
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Volume
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1728 cu. inches = 1 cubic foot
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27 cu. feet = 1 cubic yard
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Capacity (Dry) Capacity (Liquid)
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16 fluid ounces = 1 pint
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2 pints = 1 quart 4 gills = 1 pint
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8 quarts = 1 peck 2 pints = 1 quart
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4 pecks = 1 bushel 4 quarts = 1 gallon (8 pints)
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Mass
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437.5 grains = 1 ounce Troy Weights
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16 ounces = 1 pound (7000 grains) 24 grains = 1 pennyweight
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14 pounds = 1 stone 20 pennyweights = 1 ounce (480 grains)
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100 pounds = 1 hundredweight [cwt] 12 ounces = 1 pound (5760 grains)
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20 cwt = 1 ton (2000 pounds)
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Apothecaries' Measures Apothecaries' Weights
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60 minims = 1 fl.dram 20 grains = 1 scruple
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8 fl.drams = 1 fl.ounce 3 scruples = 1 dram
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16 fl.ounces = 1 pint 8 drams = 1 ounce (480 grains)
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12 ounces = 1 pound (5760 grains)
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As with the UK system these measures were originally defined by physical
|
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standard measures - the yard, the pound, the gallon and the bushel.They are now
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all defined by reference to the S I measures of the metre, the kilogram and the
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litre. These equivalent measures are exact.
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1 yard = 0.9144 metres - same as UK
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1 pound = 0.453 592 37 kilograms - same as UK
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1 gallon (liquid) = 3.785 411 784 litres
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1 bushel = 35.239 070 166 88 litres
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Note particularly that the US gallon is a different size to the UK gallon so
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that NO liquid measures of the same name are the same size in the US and UK
|
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systems.
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Also that the ton(US) is 2000 pounds while a ton(UK) is 2240 pounds. These are
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also referred to as a short ton and long ton respectively.
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Note than in matters concerned with land measurements, for the most accurate
|
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work, it is necessary to establish whether the US survey measures are being
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used or not.
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--------------------------------------------------------------------------------
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A
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acres angstroms ares astronomical units atmospheres
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B
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barleycorns barrels (oil) bars British thermal units Btu/hour etc. bushels
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C
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calories calories per hour etc. carats, metric centigrade heat units
|
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centilitres centimetres centimetres of mercury or water centimetres per minute
|
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etc. chains (surveyors') circular inches cubic (+ any units) cubic measures per
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area cubits
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D
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decilitres denier drex dynes
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E
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ells (UK) ems (pica) ergs (energy) ergs (torque)
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F
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fathoms feet feet of water feet per hour etc. fluid ounces foot pounds-force
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foot pounds-force per minute etc. foot poundals furlongs
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G
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gallons gallons per area gigajoules gigawatts grains grains per gallon grams
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gram-force centimetres grams per area grams per cm grams per (any volume)
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H
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hands hectares hides horsepower horsepower hours hundredweights
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IJ
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inches inches of mercury or water inches of rain (by mass) inches of rain (by
|
||
volume) inches per minute etc. joules joules per hour etc.
|
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|
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K
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kilocalories kilocalories per hour etc. kilograms-force kilogram-force metres
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(energy) kilogram-force metres (torque) kilogram-force metres per hour etc.
|
||
kilogram-force per area kilograms kilograms per area kilograms per metre
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kilograms per volume kilojoules kilojoules per hour etc. kilometres kilometres
|
||
per hour etc. kilometres per litre kilonewton per square metre kilonewtons
|
||
kilopascals kilowatts kilowatt hours kips (weight) kips (force) kips per square
|
||
inch knots
|
||
|
||
L
|
||
|
||
leagues light years links (surveyors') litres
|
||
litres per area
|
||
|
||
M
|
||
|
||
Mach number megajoules meganewtons meganewtons per square metre megawatts metres
|
||
metres of water metres per second etc. microns (=micrometres) miles miles per
|
||
gallon miles per hour etc.
|
||
millibars milligrams per cm milligrams per (any volume) millilitres millimetres
|
||
of mercury or water millimetres of rain (by mass) millimetres of rain (by
|
||
volume)
|
||
|
||
N
|
||
|
||
newton metres (energy) newton metres (torque) newtons (per area) newtons
|
||
(force) newtons (weight)
|
||
|
||
O
|
||
|
||
ounces
|
||
ounces per inch ounces per area ounces per volume
|
||
|
||
PQ
|
||
|
||
parsecs pascals perch (=rods or poles) picas pints points (printers') poundals
|
||
poundals per square foot pounds pounds per area pounds per foot pounds per
|
||
volume pounds-force pound-force inches pounds-force per area quarts
|
||
|
||
R
|
||
|
||
roods
|
||
|
||
S
|
||
|
||
slugs (or g-pounds) stones square (+ any units) squares (of timber) sthenes
|
||
|
||
T
|
||
|
||
tex therms tonnes ton-force metres tonnes-force tonnes-force per area tonnes
|
||
per hectare tonnes per km tonnes per volume ton-force feet tons tons-force
|
||
tons-force per area tons per acre tons per mile tons per volume townships troy
|
||
ounce
|
||
|
||
UVW
|
||
|
||
watt second watt hours watts
|
||
|
||
XYZ
|
||
|
||
yards yards per hour etc.
|
||
|
||
--------------------------------------------------------------------------------
|
||
|
||
Length
|
||
|
||
The S I unit of length is the metre. To change any of these other units of
|
||
length into their equivalent values in metres use the operation and conversion
|
||
factor given. Those marked with # are exact. Other values are given to an
|
||
appropriate degree of accuracy. Where some uncertainty is indicated it means
|
||
that a good idea of the size of the unit can be given but that a better value
|
||
would depend upon knowing the period and/or culture in which the unit was being
|
||
used.
|
||
|
||
angstroms divide by 10 000 000 000 #
|
||
astronomical units x 149 598 550 000
|
||
barleycorns x 0.008 467
|
||
centimetres x 0.01 #
|
||
chains (surveyors') x 20.1168 #
|
||
cubits x (0.45 to 0.5)
|
||
ells (UK) x 0.875 (but many variations)
|
||
ems (pica) x 0.004 233 3
|
||
fathoms x 1.8288 #
|
||
|
||
feet (UK and US) x 0.3048 #
|
||
feet (US survey) x 0.304 800 609 6
|
||
furlongs x 201.168 #
|
||
hands x 0.106 #
|
||
inches x 0.0254 #
|
||
kilometres x 1000 #
|
||
leagues x (4000 to 5000)
|
||
light years x 9 460 500 000 000 000
|
||
links (surveyors') x 0.201 168 #
|
||
metres [m] 1
|
||
microns (=micrometres) x 0.000 001 #
|
||
miles (UK and US) x 1609.344 #
|
||
miles (nautical) x 1852 #
|
||
parsecs x 30 856 770 000 000 000
|
||
perch (=rods or poles) x 5.0292 #
|
||
picas (computer) x 0.004 233 333
|
||
picas (printers') x 0.004 217 518
|
||
points (computer) x 0.000 352 777 8
|
||
points (printers') x 0.000 351 459 8
|
||
yards x 0.9144 #
|
||
Note than in matters concerned with land measurements, for the most accurate
|
||
work, it is necessary to establish whether the US survey measures are being
|
||
used or not.
|
||
|
||
--------------------------------------------------------------------------------
|
||
|
||
Area
|
||
|
||
The S I unit of area is the square metre. To change any of these other units of
|
||
area into their equivalent values in square metres use the operation and
|
||
conversion factor given. Those marked with # are exact. Other values are given
|
||
to an appropriate degree of accuracy. Where some uncertainty is indicated it
|
||
means that a good idea of the size of the unit can be given but that a better
|
||
value would depend upon knowing the period and/or culture in which the unit was
|
||
being used.
|
||
|
||
acres x 4046.856 422 4 #
|
||
ares x 100 #
|
||
circular inches x 0.000 506 707 479
|
||
hectares x 10 000 #
|
||
hides x 485 000 (with wide variations)
|
||
roods x 1011.714 105 6 #
|
||
square centimetres x 0.000 1 #
|
||
square feet (UK and US) x 0.092 903 04 #
|
||
square feet (US survey) x 0.092 903 411 613
|
||
square inches x 0.000 645 16 #
|
||
square kilometres x 1 000 000 #
|
||
square metres 1
|
||
square miles x 2 589 988.110 336 #
|
||
square millimetres x 0.000 001 #
|
||
squares (of timber) x 9.290 304 #
|
||
square rods (or poles) x 25.292 852 64 #
|
||
square yards x 0.836 127 36 #
|
||
townships x 93 239 571.972
|
||
Note than in matters concerned with land measurements, for the most accurate
|
||
work, it is necessary to establish whether the US survey measures are being
|
||
used or not.
|
||
|
||
--------------------------------------------------------------------------------
|
||
|
||
Volume or Capacity
|
||
|
||
The S I unit of volume is the cubic metre. However, this seems to be much less
|
||
used than the litre (1000 litres = 1 cubic metre).To change any of these other
|
||
units of volume into their equivalent values in litres use the operation and
|
||
conversion factor given. Those marked with # are exact. Other values are given
|
||
to an appropriate degree of accuracy.
|
||
The litre. There can be some ambiguity about the size of the litre. In 1901 it
|
||
was defined by reference to a kilogram of pure water under certain particular
|
||
conditions. (This was similar to the way the old UK gallon was set.) In 1964 it
|
||
was re-defined as a common usage term for a cubic decimetre. They differ very
|
||
slightly and for really accurate work, to avoid any possible confusion, it is
|
||
recommended that the litre is not used . It is used here as being a cubic
|
||
decimetre.
|
||
|
||
barrels (oil) x 158.987 294 928 #
|
||
bushels (UK) x 36.368 72 #
|
||
bushels (US) x 35.239 070 166 88 #
|
||
centilitres x 0.01 #
|
||
cubic centimetres x 0.001 #
|
||
cubic decimetres 1
|
||
cubic decametres x 1 000 000 #
|
||
cubic feet x 28.316 846 592 #
|
||
cubic inches x 0.016 387 064 #
|
||
|
||
cubic metres x 1000 #
|
||
cubic millimetres x 0.000 001 #
|
||
cubic yards x 764.554 857 984 #
|
||
decilitres x 0.1 #
|
||
fluid ounces (UK) x 0.028 413 062 5 #
|
||
fluid ounces (US) x 0.029 573 534 562 5 #
|
||
gallons (UK) x 4.546 09 #
|
||
gallons, dry (US) x 4.404 883 770 86 #
|
||
gallons, liquid (US) x 3.785 411 784 #
|
||
litres [l or L] 1
|
||
litres (1901 - 1964) x 1.000 028
|
||
millitres x 0.001 #
|
||
pints (UK) x 0.568 261 25 #
|
||
pints, dry (US) x 0.550 610 471 357 5 #
|
||
pints, liquid (US) x 0.473 176 473 #
|
||
quarts (UK) x 1.136 522 5 #
|
||
quarts, dry (US) x 1.101 220 942 715 #
|
||
quarts, liquid (US) x 0.946 352 946 #
|
||
--------------------------------------------------------------------------------
|
||
|
||
Mass (or Weight)
|
||
|
||
The S I unit of mass is the kilogram. To change any of these other units of
|
||
mass into their equivalent values in kilograms use the operation and conversion
|
||
factor given. Those marked with # are exact. Other values are given to an
|
||
appropriate degree of accuracy.
|
||
|
||
carats, metric x 0.000 2 #
|
||
grains x 0.000 064 798 91 #
|
||
grams x 0.001 #
|
||
hundredweights, long x 50.802 345 44 #
|
||
hundredweights, short x 45.359 237 #
|
||
kilograms [kg] 1
|
||
ounces, avoirdupois x 0.028 349 523 125 #
|
||
ounces, troy x 0.031 103 476 8 #
|
||
pounds x 0.453 592 37 #
|
||
slugs (or g-pounds) x 14.593 903
|
||
stones x 6.350 293 18 #
|
||
tons (UK or long) x 1016.046 908 8 #
|
||
tons (US or short) x 907.184 74 #
|
||
tonnes x 1000 #
|
||
--------------------------------------------------------------------------------
|
||
|
||
Line density
|
||
|
||
Line density is a measure of mass per unit length. The S I compatible unit of
|
||
line density is kilograms/metre. A major use of line density is in the textile
|
||
industry to indicate the coarseness of a yarn or fibre. For that purpose the SI
|
||
unit is rather large so the preferred unit there is the tex. (1 tex = 1
|
||
gram/kilometre) To change any of these other units of line density into their
|
||
equivalent values in kilograms/metre use the operation and conversion factor
|
||
given. Those marked with # are exact. Other values are given to an appropriate
|
||
degree of accuracy.
|
||
|
||
denier divide by 9 000 000 #
|
||
drex divide by 10 000 000 #
|
||
grams/centimetre divide by 10 #
|
||
grams/kilometre (tex) divide by 1 000 000 #
|
||
grams/metre divide by 1000 #
|
||
grams/millimetre 1
|
||
kilograms/kilometre divide by 1000 #
|
||
|
||
kilograms/metre 1
|
||
|
||
milligrams/centimetre divide by 10 000 #
|
||
milligrams/millimetre divide by 1000 #
|
||
ounces/inch x 1.116 125
|
||
ounces/foot x 0.093 01
|
||
pounds/inch x 17.858
|
||
pounds/foot x 1.488 164
|
||
pounds/yard x 0.496 055
|
||
pounds/mile x 0.000 281 849
|
||
tex divide by 1 000 000 #
|
||
tons(UK)/mile x 0.631 342
|
||
tons(US)/mile x 0.563 698
|
||
tonnes/kilometre 1
|
||
--------------------------------------------------------------------------------
|
||
|
||
Density
|
||
|
||
Density is the shortened term generally used in place of the more accurate
|
||
description volumetric density.It is a measure of mass per unit volume. The S I
|
||
compatible unit of density is kilograms/cubic metre. However, this a rather
|
||
large unit for most purposes (iron is over 7000, wood is about 600 and even
|
||
cork is over 200). A much more useful size of unit is kilograms/litre (for
|
||
which the previous values then become 7, 0.6 and 0.2 respectively). This unit
|
||
also has the great advantage of being numerically unchanged for grams/cubic
|
||
centimetre and tonnes/cubic metre (or megagrams/cubic metre). To change any of
|
||
these other units of density into their equivalent values in kilograms/litre
|
||
use the operation and conversion factor given. Those marked with # are exact.
|
||
Other values are given to an appropriate degree of accuracy.
|
||
|
||
grains/gallon(UK) divide by 70 156
|
||
grains/gallon(US) divide by 58 418
|
||
grams/cubic centimetre 1
|
||
grams/litre divide by 1000 #
|
||
grams/millilitre 1
|
||
kilograms/cubic metre divide by 1000 #
|
||
megagrams/cubic metre 1
|
||
milligrams/millitre divide by 1000 #
|
||
milligrams/litre divide by 1 000 000 #
|
||
|
||
kilograms/litre 1
|
||
|
||
ounces/cubic inch x 1.729 994 044
|
||
ounces/gallon(UK) x 0.006 236 023
|
||
ounces/gallon(US) x 0.007 489 152
|
||
pounds/cubic inch x 27.679 904
|
||
pounds/cubic foot x 0.016 018 463
|
||
pounds/gallon(UK) x 0.099 776 373
|
||
pounds/gallon(US) x 0.119 826 427
|
||
tonnes/cubic metre 1
|
||
tons(UK)/cubic yard x 1.328 939 184
|
||
tons(US)/cubic yard x 1.186 552 843
|
||
--------------------------------------------------------------------------------
|
||
|
||
Energy or work
|
||
|
||
There is a lot of room for confusion in some of the units used here. The
|
||
calorie can take 5 different values and, while these do not vary by very much,
|
||
for accurate work it is necessary to specify which calorie is being used.
|
||
The 5 calories are known as the International Table calorie - cal(IT); the
|
||
thermochemical calorie - cal(th); the mean calorie - cal(mean); the 15 degree C
|
||
calorie - cal(15C); and the 20 degree C calorie - cal(20C).
|
||
As a further complication, in working with food and expressing nutritional
|
||
values, the unit of a Calorie (capital C) is often used to represent 1000
|
||
calories, and again it is necessary to specify which calorie is being used for
|
||
that.
|
||
The British thermal unit (Btu) can also take different values and they are
|
||
named in a similar way to the calorie, that is Btu (IT), (th), etc. Also note
|
||
that the therm is 100 000 Btu so its exact size depends on which Btu is being
|
||
used.
|
||
|
||
The S I unit of energy or work is the joule. To change any of these other units
|
||
of energy or work into their equivalent values in joules use the operation and
|
||
conversion factor given. Those marked with # are exact. Other values are given
|
||
to an appropriate degree of accuracy.
|
||
|
||
British thermal units(IT)x 1055.056
|
||
Btu (th) x 1054.350
|
||
Btu (mean) x 1055.87
|
||
calories - cal (IT) x 4.1868 #
|
||
- cal (th) x 4.184 #
|
||
- cal (mean) x 4.190 02
|
||
- cal (15C) x 4.185 80
|
||
- cal (20C) x 4.181 90
|
||
Calorie (food) x 4186 (approx.)
|
||
centigrade heat units x 1900.4
|
||
ergs divide by 10 000 000 #
|
||
foot pounds-force x 1.355 817
|
||
foot poundals x 0.042 140
|
||
gigajoules [GJ] x 1000 000 000 #
|
||
horsepower hours x 2 684 520 (approx.)
|
||
joules [J] 1
|
||
kilocalories (IT) x 4186.8 #
|
||
kilocalories (th) x 4184 #
|
||
kilogram-force metres x 9.806 65 #
|
||
kilojoules [kJ] x 1000 #
|
||
kilowatt hours [kWh] x 3 600 000 #
|
||
megajoules [MJ] x 1 000 000 #
|
||
newton metres [Nm] x 1 #
|
||
therms x 105 500 000 (approx.)
|
||
watt seconds [Ws] 1
|
||
watt hours [Wh] x 3600 #
|
||
--------------------------------------------------------------------------------
|
||
|
||
Force
|
||
|
||
The S I unit of force is the newton. To change any of these other units of
|
||
force into their equivalent values in newtons use the operation and conversion
|
||
factor given. Those marked with # are exact. Other values are given to an
|
||
appropriate degree of accuracy.
|
||
|
||
dynes divide by 100 000 #
|
||
kilograms force x 9.806 65 #
|
||
kilonewtons [kN] x 1000 #
|
||
kips x 4448.222
|
||
meganewtons [MN] x 1 000 000 #
|
||
|
||
newtons [N] 1
|
||
|
||
pounds force x 4.448 222
|
||
poundals x 0.138 255
|
||
sthenes (=kN) x 1000
|
||
tonnes force x 9806.65 #
|
||
tons(UK) force x 9964.016
|
||
tons(US) force x 8896.443
|
||
--------------------------------------------------------------------------------
|
||
|
||
Fuel Consumption
|
||
|
||
Fuel consumption of any means of transport (car, aeroplane, ship etc.) that
|
||
uses fuel is a measure giving the relationship between the distance travelled
|
||
for an amount of fuel used. The most common example is the car where it is
|
||
usually expressed (in English-speaking countries) in miles per gallon.
|
||
It could also be expressed in gallons per mile. However, for a car the latter
|
||
method gives a rather small figure: 35 miles per gallon is about 0.0286 gallons
|
||
per mile. In that case it would be better to give a figure for 100 miles, so it
|
||
would be 2.86 gallons per 100 miles. That is the metric way of expressing fuel
|
||
consumption - as litres per 100 kilometres.
|
||
From regular enquiries it appears that in real life people are using all sorts
|
||
of ways of expressing their fuel consumption, so this section (unlike all the
|
||
others) tries to cover as many ways as possible. All the values are given to an
|
||
accuracy of 4 significant figures.
|
||
|
||
To change into
|
||
miles per gallon (UK) miles per gallon (US) multiply by 0.833
|
||
miles per gallon (UK) miles per litre multiply by 0.22
|
||
miles per litre miles per gallon (UK) multiply by 4.456
|
||
miles per gallon (UK) kilometres per litre multiply by 0.354
|
||
|
||
miles per gallon (US) miles per gallon (UK) multiply by 1.2
|
||
miles per gallon (US) miles per litre multiply by 0.2642
|
||
miles per litre miles per gallon (US) multiply by 3.785
|
||
miles per gallon (US) kilometres per litre multiply by 0.4251
|
||
|
||
X miles per gallon gallons per 100 miles: divide 100 by X
|
||
(both gallons must of the same type)
|
||
|
||
X miles per gallon (UK) litres per 100 km: divide 282.5 by X
|
||
X miles per gallon (US) litres per 100 km: divide 235.2 by X
|
||
X km per litre litres per 100 km: divide 100 by X
|
||
X miles per litre litres per 100 km: divide 62.14 by X
|
||
--------------------------------------------------------------------------------
|
||
|
||
Power
|
||
|
||
Since power is a measure of the rate at which work is done, the underlying
|
||
units are those of work or energy, and that section should be looked at for
|
||
explanations concerning the calorie and Btu. In this section the (IT) values
|
||
have been used.
|
||
In this section it is the horsepower which provides confusion. Just like the
|
||
calorie, it can take 5 different values, and these are identified as necessary
|
||
by the addition of (boiler), (electric), (metric), (UK) and (water). Unlike the
|
||
calorie (whose 5 values are reasonably close to each other), the horsepower has
|
||
4 which are close and 1 (boiler) which is considerably different - it is about
|
||
13 times bigger than the others - but it seems to be very little used.
|
||
|
||
The S I unit of power is the watt. To change any of these other units of energy
|
||
or work into their equivalent values in watts use the operation and conversion
|
||
factor given. Those marked with # are exact. Other values are given to an
|
||
appropriate degree of accuracy.
|
||
|
||
Btu/hour x 0.293 071
|
||
Btu/minute x 17.584 267
|
||
Btu/second x 1055.056
|
||
calories/hour x 0.001 639
|
||
calories/minute x 0.069 78
|
||
calories/second x 4.1868 #
|
||
ft lb-force/minute x 0.022 597
|
||
ft lb-force/second x 1.355 82
|
||
gigawatts [GW] x 1 000 000 000
|
||
horsepower (electric) x 746 #
|
||
horsepower (metric) x 735.499
|
||
watts [W] 1
|
||
joules/hour divide by 3600 #
|
||
joules/minute divide by 60 #
|
||
joules/second 1
|
||
kilocalories/hour x 1.163
|
||
kilocalories/minute x 69.78
|
||
kg-force metres/hour x 0.002 724
|
||
kg-force metres/minute x 0.163 444
|
||
kilowatts [kW] x 1000 #
|
||
megawatts [MW] x 1 000 000 #
|
||
--------------------------------------------------------------------------------
|
||
|
||
Pressure or Stress
|
||
|
||
The S I unit of pressure is the pascal. The units of pressure are defined in
|
||
the same way as those for stress - force/unit area. To change any of these
|
||
other units of pressure (or stress) into their equivalent values in pascals use
|
||
the operation and conversion factor given. Those marked with # are exact. Other
|
||
values are given to an appropriate degree of accuracy. Measures based on water
|
||
assume a density of 1 kg/litre - a value which rarely matched in the real
|
||
world, though the error is small.
|
||
|
||
atmospheres x 101 325 #
|
||
bars x 100 000 #
|
||
centimetres of mercury x 1333.22
|
||
centimetres of water x 98.066 5 #
|
||
feet of water x 2989.066 92 #
|
||
hectopascals [hPa] x 100 #
|
||
inches of water x 249.088 91 #
|
||
inches of mercury x 3386.388
|
||
kg-force/sq.centimetre x 98 066 5 #
|
||
kg-force/sq.metre x 9.806 65 #
|
||
kilonewton/sq.metre x 1000 #
|
||
kilopascal [kPa] x 1000 #
|
||
kips/sq.inch x 6 894 760
|
||
meganewtons/sq.metre x 1 000 000 #
|
||
metres of water x 9806.65 #
|
||
millibars x 100 #
|
||
|
||
pascals [Pa] 1
|
||
|
||
millimetres of mercury x 133.322
|
||
millimetres of water x 9.806 65 #
|
||
newtons/sq.centimetre x 10 000
|
||
newtons/sq.metre 1
|
||
newtons/sq.millimetre x 1 000 000 #
|
||
pounds-force/sq.foot x 47.880
|
||
pounds-force/sq.inch x 6894.757
|
||
poundals/sq.foot x 1.448 16
|
||
tons(UK)-force/sq.foot x 107 251
|
||
tons(UK)-force/sq.inch x 15 444 256
|
||
tons(US)-force/sq.foot x 95 760
|
||
tons(US)-force/sq.inch x 13 789 500
|
||
tonnes-force/sq.cm x 98 066 500 #
|
||
tonnes-force/sq.metre x 9806.65 #
|
||
--------------------------------------------------------------------------------
|
||
|
||
Speed
|
||
|
||
The S I compatible unit of speed is metres/second. To change any of these other
|
||
units of speed into their equivalent values in metres/second use the operation
|
||
and conversion factor given. Those marked with # are exact. Other values are
|
||
given to an appropriate degree of accuracy.
|
||
|
||
centimetres/minute divide by 6000 #
|
||
centimetres/second divide by 100 #
|
||
feet/hour divide by 11 811
|
||
feet/minute x 0.005 08 #
|
||
feet/second x 0.3048 #
|
||
inches/minute divide by 2362.2
|
||
inches/second x 0.0254 #
|
||
kilometres/hour divide by 3.6 #
|
||
kilometres/second x 1000 #
|
||
knots x 0.514 444
|
||
Mach number x 331.5
|
||
metres/hour divide by 3600 #
|
||
metres/minute divide by 60 #
|
||
|
||
metres/second [m/s] 1
|
||
|
||
miles/hour x 0.447 04 #
|
||
miles/minute x 26.8224 #
|
||
miles/second x 1609.344 #
|
||
yards/hour divide by 3937
|
||
yards/minute x 0.015 24 #
|
||
yards/second x 0.9144 #
|
||
--------------------------------------------------------------------------------
|
||
|
||
Spread Rate (by mass)
|
||
|
||
The spread rate of a substance is a measure of how much of it there is covering
|
||
a unit area. The 'how much' can be measured by volume or by mass. The S I
|
||
compatible unit of spread rate by mass is kilograms/square metre. It is also a
|
||
measure of area density (mass/unit area) and is similar to - but not the same
|
||
as - pressure, which is force/unit area. For the rainfall conversions a density
|
||
of 1 kg/litre has been assumed. To change any of these other units of spread
|
||
rate into their equivalent values in kilograms/square metre use the operation
|
||
and conversion factor given. Those marked with # are exact. Other values are
|
||
given to an appropriate degree of accuracy. The conversion for rainfall assumes
|
||
a density of 1 kg/litre which is accurate enough for all practical purposes.
|
||
|
||
grams/sq.centimetre x 10 #
|
||
grams/sq.metre divide by 1000 #
|
||
inches of rainfall x 2.54
|
||
kilograms/hectare divide by 10 000 #
|
||
kilograms/sq.centimetre x 10 000 #
|
||
milligrams/sq.metre divide by 1000 #
|
||
millimetres of rainfall 1
|
||
|
||
kilograms/sq.metre 1
|
||
|
||
ounces/sq.foot x 0.305 152
|
||
ounces/sq.inch x 43.942
|
||
ounces/sq.yard divide by 49.494
|
||
pounds/acre divide by 8921.791
|
||
pounds/sq.foot x 4.882 428
|
||
pounds/sq.inch x 703.07
|
||
pounds/sq.yard x 0.542 492
|
||
tonnes/hectare divide by 10 #
|
||
tons(UK)/acre divide by 3.982 942
|
||
tons(US)/acre divide by 4.460 896
|
||
--------------------------------------------------------------------------------
|
||
|
||
Spread Rate (by volume)
|
||
|
||
The spread rate of a substance is a measure of how much of it there is covering
|
||
a unit area. The 'how much' can be measured by volume or by mass. The S I
|
||
compatible unit of spread rate by volume is cubic metres/square metre. However,
|
||
this is a rather large unit for most purposes and so litres/square metre is
|
||
often preferred. To change any of these other units of spread rate into their
|
||
equivalent values in litres/square metre use the operation and conversion
|
||
factor given. Those marked with # are exact. Other values are given to an
|
||
appropriate degree of accuracy.
|
||
|
||
cubic feet/acre divide by 142.913
|
||
cubic inches/sq.yard divide by 51.024
|
||
cubic yards/sq.mile divide by 3387.577
|
||
cubic metres/hectare divide by 10 #
|
||
cubic metres/sq.km divide by 1000 #
|
||
cubic metres/sq.metre x 1000 #
|
||
fl. ounces(UK)/sq.yard divide by 29.428
|
||
|
||
litres/square metre 1
|
||
|
||
gallons(UK)/acre divide by 890.184
|
||
gallons(US)/acre divide by 1069.066
|
||
gallons(UK)/hectare divide by 2199.692
|
||
gallons(US)/hectare divide by 2641.721
|
||
inches of rainfall x 25.4 #
|
||
litres/hectare divide by 10 000 #
|
||
millitres/sq.metre divide by 1000 #
|
||
millimetres of rainfall 1
|
||
--------------------------------------------------------------------------------
|
||
|
||
Torque
|
||
|
||
The S I compatible unit of torque is the newton metre. To change any of these
|
||
other units of torque into their equivalent values in newton metres use the
|
||
operation and conversion factor given. Those marked with # are exact. Other
|
||
values are given to an appropriate degree of accuracy.
|
||
|
||
dyne centimetres divide by 10 000 000 #
|
||
gram-force centimetres x 0.000 098 066 5 #
|
||
kg-force centimetres x 0.098 066 5 #
|
||
kg-force metres x 9.806 65 #
|
||
newton centimetres divide by 100 #
|
||
|
||
newton metres [Nm] 1
|
||
|
||
ounce-force inches divide by 141.612
|
||
pound-force inches x 0.112 984
|
||
pound-force feet x 1.355 818
|
||
poundal feet x 0.042 140
|
||
ton(UK)-force feet x 3 037.032
|
||
ton(US)-force feet x 2 711.636
|
||
tonne-force metres x 9 806.65 #
|
||
--------------------------------------------------------------------------------
|
||
|