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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 0.875Return to the top of this document(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 0.3048 006 096 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] 1microns (=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 x 0.004 233 333 points (printers') x 0.000 352 777 yards x 0.9144 #

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 000Return to the top of this document(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 1square 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

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.

barrels (oil) x 158.987 294 928 # bushels (UK) x 36.368 72 # bushels, dry (US) x 35.239 070 166 88 # centilitres x 0.01 # cubic centimetres x 0.001 # cubic decimetres 1 cubic dekametres 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 #Return to the top of this documentlitres [l or L] 1millitres 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 #

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 #Return to the top of this documentkilograms [kg] 1kips x 453.592 37 # newtons divide by 9.806 65 # 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 0.068 521 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 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 #Return to the top of this documentkilograms/metre 1milligrams/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 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. 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 # milligrams/millitre divide by 1000 # milligrams/litre divide by 1 000 000 #Return to the top of this documentkilograms/litre 1ounces/cubic inch x 1.729 994 044 ounces/gallon(UK) x 0.006 236 023 ounces/gallon(US) x 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

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 divide by 1055.056 # calories divide by 4.1868 # 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 520Return to the top of this documentjoules [J] 1kilocalories divide by 4186.8 # 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 105 575 000 # watt seconds [Ws] 1 watt hours [Wh] x 3600 #

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 #Return to the top of this documentnewtons [N] 1pounds 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 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.

The rules below give a way of converting some of these different forms of measurement of fuel consumption. 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 0.4251Return to the top of this documentXmiles per gallon gallons per 100 miles, divide 100 byX(both gallons must of the same type)Xmiles per gallon (UK) litres per 100 miles, divide 282.5 byXXmiles per gallon (US) litres per 100 miles, divide 235.2 byX

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 17.584 263 Btu/second x 1055.055 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 x 745.7Return to the top of this documentwatts [W] 1joules/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 kiowatts [kW] x 1000 # megawatts [MW] x 1 000 000 #

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.

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 # 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 #Return to the top of this documentpascals [Pa] 1millimetres 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 #

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 0.0005 08 # feet/second x 0.3048 # inches/minute divide by 2362.2 inches/second x 0.0254 # kilometres/hour x 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 #Return to the top of this documentmetres/second [m/s] 1miles/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 #

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.

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 1Return to the top of this documentkilograms/sq.metre 1ounces/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

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 29.428Return to the top of this documentlitres/square metre 1gallons(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

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.

ergs (= dyne cm) 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 5 # newton centimetres divide by 100 #Return to the top of this documentnewton metres [Nm] 1ounce-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 #

**Conversion Tables of Units for Science and Engineering** by Ari L Horvath

Macmillan Reference Books, London, 1986 (147 pages)

ISBN 0 333 40857 8

Probably the most comprehensive set of conversion factors in print, covering both old and modern units. There are 77 tables covering categories from Length to Radiation dosage. The Length table alone lists 107 units together with the conversion factors needed to change each one into metres.

**The Dent Dictionary of Measurement** by Darton and Clark

J M Dent, London, 1994 (538 pages)

ISBN 0 460 861379

Very comprehensive coverage of all kinds of units (including currencies), ordered in conventional dictionary form, and giving several conversion factors.

**The Economist Desk Companion**

Random Century, London, 1992 (272 pages)

ISBN 0 7126 9816 7

A handy compendium of units used in Science, Medicine, Engineering, Industry, Commerce, Finance and many other places, together with all the necessary conversion factors. There is also much other incidental (but related) information.

**The Encyclopaedia Britannica**

The modern E B has many references to units, but extensive use needs to be made of the index to find them all. It gives a wide selection of weights and measures from countries around the world and the appropriate conversion factors.

**World Weights and Measures**

Statistical Office of the United Nations, New York 1955 (225 pages)

A very comprehensive survey of each country in the world (as it was then) from Aden to Zanzibar, giving the units used in each for Length, Area and Capacity with their British and Metric equivalents. There is an appendix on the measures used for selected commodities. Currencies are also given. The indexes are very thorough.

**The Weights and Measures of England** by R D Connor

H M S O, London, 1987 (422 pages)

ISBN 0 460 86137 9

A scholarly and detailed account of the history of the development of the British (Imperial) system of weights and measures from the earliest times.

**British Weights and Measures** by R E Zupko

*A history from Antiquity to the Seventeenth Century*

The University of Wisconsin Press, 1977 [248 pages]

ISBN 0 299 07340 8

The actual history occupies only 100 pages. There is then an extensive list of the various units used in commerce, tables of many pre-Imperial units, a long list of pre-metric measures used in Europe together with their British and metric equivalents, and nearly 40 pages giving other sources.

**International Standards Organisation [I S O]**

This organisation (based in switzerland) is responsible for the world-wide publication of standards for just about anything for which standards can be set.

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Last Updated: January **26,
2001**