Cleave Books
A Dictionary of Units ~ Part 1
by Frank Tapson

This part provides a summary of most of the units of measurement to be found in use around the world today (and a few of historical interest), and the conversion factors needed to change them into a 'standard' unit of the SI.

A general account of systems of measurement is given in Part 2

 Here the units may be found either by looking under the in which they are used, (length energy etc.) category or by picking one unit from an alphabetically ordered list of units. There is a Summary Table of the most often required Conversion Factors. There are NO units of currency. Finally there are some notes on this material . A separate document covers the most FAQ and other measures.

Or, to get a Conversion Calculator, select required category
from this table

 Conversion CalculatorsAny problems with any of these read the FAQ Length Area Volume Mass Temperature Feet & Inches Angles Pounds & Ounces Units of Alcohol Density Pressure& Stress Speed FuelConsumption Power or ONE calculator just for Changing Prefixes Energy(Work) Flow Rateby Mass        by Volume Force Torque Specific Energy by Mass         by Volume(Calorific Value) Spread Rateby Mass        by Volume(including Rainfall) Concentration Line Density(inc. Textiles) Area Density Acceleration ViscosityDynamic        Kinematic Specific Heat Capacityby Mass        by Volume Heat FluxDensity ThermalConductivity ThermalConductance There is a Selection of Other Calculators also available

Summary table of conversion factors most often required
x means 'multiply by' . . . / means 'divide by' . . . # means it is an exact value
All other values given to an appropriate degree of accuracy.
 To change . . into . . do this . . To change . . into . . do this . . acres hectares x 0.4047 kilograms ounces x 35.3 acres sq. kilometres / 247 kilograms pounds x 2.2046 acres sq. metres x 4047 kilograms tonnes / 1000 # acres sq. miles / 640 # kilograms tons (UK/long) / 1016 barrels (oil) cu.metres / 6.29 kilograms tons (US/short) / 907 barrels (oil) gallons (UK) x 34.97 kilometres metres x 1000 # barrels (oil) gallons (US) x 42 # kilometres miles x 0.6214 barrels (oil) litres x 159 litres cu.inches x 61.02 centimetres feet / 30.48 # litres gallons (UK) x 0.2200 centimetres inches / 2.54 # litres gallons (US) x 0.2642 centimetres metres / 100 # litres pints (UK) x 1.760 centimetres millimetres x 10 # litres pints (US liquid) x 2.113 cubic cm cubic inches x 0.06102 metres yards / 0.9144 # cubic cm litres / 1000 # metres centimetres x 100 # cubic cm millilitres x 1 # miles kilometres x 1.609 cubic feet cubic inches x 1728 # millimetres inches / 25.4 # cubic feet cubic metres x 0.0283 ounces grams x 28.35 cubic feet cubic yards / 27 # pints (UK) litres x 0.5683 cubic feet gallons (UK) x 6.229 pints (UK) pints (US liquid) x 1.201 cubic feet gallons (US) x 7.481 pints (US liquid) litres x 0.4732 cubic feet litres x 28.32 pints (US liquid) pints (UK) x 0.8327 cubic inches cubic cm x 16.39 pounds kilograms x 0.4536 cubic inches litres x 0.01639 pounds ounces x 16 # cubic metres cubic feet x 35.31 To change . . into . . do this . . To change . . into . . do this . . square cm sq. inches x 0.1550 feet centimetres x 30.48 # square feet sq. inches x 144 # feet metres x 0.3048 # square feet sq. metres x 0.0929 feet yards / 3 # square inches square cm x 6.4516 # fl.ounces (UK) fl.ounces (US) x 0.961 square inches square feet / 144 # fl.ounces (UK) millilitres x 28.41 square km acres x 247 fl.ounces (US) fl.ounces (UK) x 1.041 square km hectares x 100 # fl.ounces (US) millilitres x 29.57 square km square miles x 0.3861 gallons pints x 8 # square metres acres / 4047 gallons (UK) cubic feet x 0.1605 square metres hectares / 10 000 # gallons (UK) gallons (US) x 1.2009 square metres x 10.76 gallons (UK) litres x 4.54609 # square metres square yards x 1.196 gallons (US) cubic feet x 0.1337 square miles acres x 640 # gallons (US) gallons (UK) x 0.8327 square miles hectares x 259 gallons (US) litres x 3.785 square miles square km x 2.590 grams kilograms / 1000 # square yards square metres / 1.196 grams ounces / 28.35 tonnes kilograms x 1000 # hectares acres x 2.471 tonnes tons (UK/long) x 0.9842 hectares square km / 100 # tonnes tons (US/short) x 1.1023 hectares square metres x 10000 # tons (UK/long) kilograms x 1016 hectares square miles / 259 tons (UK/long) tonnes x 1.016 hectares square yards x 11 960 tons (US/short) kilograms x 907.2 inches centimetres x 2.54 # tons (US/short) tonnes x 0.9072 inches feet / 12 # yards metres x 0.9144 #
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## Categories of Units

### density, areadensity, linedensity, volumeenergyforcefuel consumptionmass per unit lengthmass per unit areamass per unit volume

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## List of Units

 Units are listed in alphabetical order. Scanning can be speeded up by selectingthe initial letter of the unit from these individual letters or groups A - B - C - D - E - F - G - H - IJ - K - L - M N - O - PQ - R - S - T - UVW - XYZ
 A to K A acres angstroms ares astronomical units atmospheres B barleycorns barrels (oil) bars British thermal units Btu/hour etc. bushels C calories calories per hour etc. carats, metric Celsius centigrade centigrade heat units centilitres centimetres centimetres of mercury or water centimetres per minute etc. chains (surveyors') circular inches cubic (+ any units) cubic measures per area cubits D decilitres denier drex dynes E ells (UK) ems (pica) ergs (energy) ergs (torque) F Fahrenheit fathoms feet feet of water feet per hour etc. fluid ounces foot pounds-force foot pounds-force per minute etc. foot poundals furlongs G gallons gallons per area gigajoules gigawatts grains grains per gallon grams gram-force centimetres grams per area grams per cm grams per (any volume) H hands hectares hides horsepower horsepower hours hundredweights IJ 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. K Kelvin kilocalories kilocalories per hour etc. kilograms-force kilogram-force metres (energy) kilogram-force metres (torque) kilogram-force metres per hour etc. kilogram-force per area kilograms kilograms per area kilograms per metre 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 (force) kips per square inch knots
 L to Z 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 Rankine Reaumur 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.
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## 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.
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.

 ```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 0.1016 # 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 # ```
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## 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. 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.

 ```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```
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## 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. When the metric system was introduced in the 1790's the litre was intended to match up with the volume occupied by 1 kilogram of pure water at a specified pressure and temperature. As the ability to measure things got better (by 100 years later) they found that there was a mismatch between the kilogram and the litre. As a result of this they had to redefine the litre (in 1901) as being 1.000028 cubic decimetres. Very handy!
This nonsense was stopped in 1964 when it was ruled that the word "litre" may be employed as a special name for the cubic decimetre, with the additional recommendation that for really accurate work, to avoid any possible confusion, the litre should not be used.
Here the litre is taken 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 0.029 573 529 562 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 millilitres 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 #```
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## 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 #```
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## Temperature

There have been five main temperature scales, each one being named after the person who invented it.
G D FAHRENHEIT (1686-1736) a German physicist, in about 1714 proposed the first practical scale. He called the freezing-point of water 32 degrees (so as to avoid negative temperatures) and the boiling-point 212 degrees.
R A F de REAUMUR (1673-1757) A French entomologist, proposed a similar scale in 1730, but set the freezing-point at 0 degrees and the boiling-point at 80 degrees. This was used quite a bit but is now obsolete.
Anders CELSIUS (1701-1744) a Swedish astronomer, proposed the 100-degree scale (from 0 to 100) in 1742. This was widely adopted as the centigrade scale. But since grades and centigrades were also measures of angle, in 1947 it officially became the Celsius scale. Also, the S I system of units gives preference to naming units after people where possible.
William Thomson, 1st Lord KELVIN (1824-1907) a Scottish mathematician and physicist, worked with J P Joule - about 1862 - to produce an absolute scale of temperature based on laws of heat rather than the freezing/boiling-points of water. This work produced the idea of 'absolute zero', a temperature below which it was not possible to go. Its value is -273.15 degrees on the Celsius scale.
William J M RANKINE (1820-1872) a Scottish engineer and scientist, promoted the Kelvin scale in its Fahrenheit form, when the equivalent value of absolute zero is -459.67 degrees Fahrenheit.
Nowadays, while scientists use the KELVIN scale, the CELSIUS scale is the preferred scale in our everyday lives. However, the Fahrenheit scale is still widely used and there frequently is a need to be able to change from one to the other.

 ```To change temperature given in Fahrenheit (F) to Celsius (C) Start with (F); subtract 32; multiply by 5; divide by 9; the answer is (C) To change temperature given in Celsius (C) to Fahrenheit (F) Start with (C); multiply by 9; divide by 5; add on 32; the answer is (F) ```
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## 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```
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## 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 70 157 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/millilitre 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 27.679 905 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```
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## 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)thermochemical calorie = cal(th)mean calorie = cal(mean)15 degree C calorie = cal(15C)20 degree C calorie = cal(20C).
Unless a clear statement is made saying otherwise, assume the IT calorie is being used.
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 1.355 818 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 # ```
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## 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```
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## 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 4.546 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 ```
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## 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 0.001 163 # 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 # ```
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## 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 is 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 107 252 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 # ```
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## 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 # ```
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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 ```
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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 # millilitres/sq.metre divide by 1000 # millimetres of rainfall 1 ```
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## 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 # ```
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## Notes

 Errors Whilst every care has been taken in the compilation of this document, and many checks have been carried out, the possibility of an error is always present in a work like this and that must be borne in mind by all users. The author would be glad to be told of any errors detected. Accuracy In a general dictionary like this it is impossible to know just what accuracy is needed by any particular user. Where the given value is an exact one then it has been signalled. In most cases other values are accurate to at least the number of significant figures shown. In some cases it might be more than that as trailing zeros have not been included. Presentation The conversion factors have mainly been presented as multipliers, but exceptions to that have been made for two reasons. First, it is easier to convey the exact value 'divide by 60' rather than the approximation 'multiply by 0.0166667' and it is more likely to be keyed in without errors if a calculator is being used. Second, most calculators accept only 8 digits, which means that 'multiply by 0.000 084 666' will become '0.000 0846' (3 significant figures) whereas 'divide by 11 811' will give the result to 6 significant figures. The appearance of a '1' needs no operator but shows that the named unit is exactly equivalent to the standard unit. Inverse usage In nearly all cases the conversion factors have been given to change 'non-standard' units into standard units of the SI. For those cases where it is necessary to do a conversion the other way it is only a matter of reversing the operation. For example to convert feet into metres you multiply by 0.3048 so, to convert metres into feet you divide by 0.3048. Following on from this it can be seen how conversions can be made between non-standard units, changing first into the standard unit and then back into the required unit. Author's Note A guiding principle behind the writing and presentation of this document has been that of clarity for non-specialist readers. To that end I have been guilty of breaking "the rules" in a few places. I am sorry that these transgressions may offend some readers but I have done so in the belief that it will be a little bit easier for many, and also help the flow of a continuous narrative. This dictionary is not meant to be encyclopaedic in its coverage, and there are many many more units which are not touched upon, but it is hoped that all 'ordinary' needs are covered. The many references to other sources, both in books and on-line should take care of anything beyond that. Finally, I must thank all of those who wrote with suggestions (and corrections!) after reading the earlier editions.

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