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CONVERSION FACTORS FOR SI/NON-SI UNITS

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This page is adapted from Conversion factors for SI and non-SI units found in each issue of the journal Agronomy (1998), published by the American Society for Agronomy. It includes conversion factors frequently needed in Agroecology. For a comprehensive set of conversion factors, see A DICTIONARY OF UNITS (http://www.ex.ac.uk/cimt/dictunit/dictunit.htm)

Length

C1 to C2 mult by Column 1 SI unit Column 2 non-SI unit C2 to C1 mult by
0.621 kilometer, km (103 m) mile, mi 1.609
1.094 meter,m yard, yd 0.914
3.28 meter, m foot, ft 0.304
1.0 micrometer, µm (10-6 m) micron, µ 1.0
3.94 x 10-2 millimeter, mm (10-3 m) inch, in 25.4
10 nanometer, nm (10-9 m) Angstrom 0.1

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Area

C1 to C2 mult by Column 1 SI or sometimes accepted unit* Column 2 non-SI unit C2 to C1 mult by
2.47 hectare*, ha
(100 x 100 m)		 acre 0.405
247 square kilometer,
km2 (103 m2) (102 ha)		 acre 4.05 x 10-3
0.386 square kilometer,
km2 (103 m2) (102 ha)		 square mile, mi2 2.590
2.47 x 10-4 square meter, m2 acre 4.05 x 103
10.76 square meter, m2 square foot, ft2 9.29 x 10-2
1.55 x 10-3 square millimeter,
mm2		 square inch, in2 645
The hectare (ha, 103 m2) is not an SI unit, but is accepted by some journals.
It is also widely used in commerce.

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Volume

C1 to C2 mult by Column 1 SI or SI acceptable unit Column 2 non-SI unit C2 to C1 mult by
9.73 x 10-3 cubic meter, m3 acre-inch 102.8
35.3 cubic meter, m3 cubic foot, ft3 2.83 x 10-2
6.10 x 104 cubic meter, m3 cubic inch, in3 1.64 x 10-5
2.84 x 10-2 liter, L (10-3 m3) bushel (US), bu 35.24
2.75 x 10-2 liter, L (10-3 m3) bushel (UK), bu 36.37
1.057 liter, L (10-3 m3) quart (liquid, US), qt 0.946
0.880 liter, L (10-3 m3) quart (liquid, UK), qt 1.137
3.54 x 10-2 liter, L (10-3 m3) cubic foot, ft3 28.3
0.265 liter, L (10-3 m3) gallon (US) 3.78
0.220 liter, L (10-3 m3) gallon (UK) 4.55
33.78 liter, L (10-3 m3) ounce (fluid), oz 2.96 x 10-2
2.11 liter, L (10-3 m3) pint (fluid) 0.473

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Mass

C1 to C2 mult by Column 1 SI or SI acceptable unit Column 2 non-SI unit C2 to C1 mult by
2.20 x 10-3 gram, g (10-3 kg) pound, lb 454
3.52 x 10-2 gram, g (10-3 kg) ounce (avpd), oz 28.4
2.205 kilogram, kg pound, lb 0.454
0.01 kilogram, kg quintal, q 100
1.10 x 10-3 kilogram, kg ton (US = 2000 lb) 907
0.984 x 10-3 kilogram, kg ton (UK = 2240 lb) 1016
1.102 megagram,
Mg or
tonne, t		 ton (US or short) 0.907
0.984 megagram,
Mg or
tonne, t		 ton (UK or long) 1.016

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Concentration

C1 to C2 mult by Column 1 SI unit Column 2 non-SI unit C2 to C1 mult by
1 centimole per kilogram
cmol kg-1		 milliequivalents per 100 grams, meq 100 g-1 1
0.1 gram per kilogram
g kg-1		 percent 10
1 milligram per kilogram, mg kg-1 parts per million, ppm 1

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Yield and rate

C1 to C2 mult by Column 1 SI or sometimes accepted unit* Column 2 non-SI unit C2 to C1 mult by
0.893 kilogram per hectare*
kg ha-1		 pound per acre , lb acre-1 1.12
1.49 x 10-2 kilogram per hectare*
kg ha-1		 bushel per acre, 60 lb 67.19
1.59 x 10-2 kilogram per hectare*
kg ha-1		 bushel per acre, 56 lb 62.71
1.86 x 10-2 kilogram per hectare*
kg ha-1		 bushel per acre, 48 lb 53.75
0.107 liter per hectare*
l ha-1		 gallon (us) per acre 9.35
893 tonnes per hectare*
t ha-1 or megagram per hectare*
Mg ha-1		 pound per acre, lb acre-1 1.12 x 10-3
0.446 tonnes per hectare*
t ha-1 or megagram per hectare*
Mg ha-1		 ton (2000 lb) per acre ton acre-1 2.24
2.24 meter per second
m s-1		 mile per hour 0.447
The hectare (ha, 103 m2) is not an SI unit, but is accepted by some journals.
It is also widely used in commerce.

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Pressure

C1 to C2 mult by Column 1 SI or SI acceptable unit Column 2 non-SI unit C2 to C1 mult by
9.90 megapascal
Mpa (106 pa)		 atmosphere 0.101
10 megapascal
Mpa (106 pa)		 bar 0.1
1.00 megagram per cubic meter, Mg m-3 gram per cubic centimeter, g cm-3 1.00
2.09 x 10-2 pascal, Pa pound per square foot lb ft-2 47.9
1.45 x 10-4 pascal, Pa pound per square inch lb in-2 6.90 x 103

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Temperature

C1 to C2 mult by Column 1 SI unit Column 2 non-SI unit C2 to C1 mult by
1.00 x (K-273) Kelvin, K Celsius, oC 1.00 x
(oC +273)
(9/5 oC)+32 Celsius, oC Farenheit, oF 5/9(oF-32)

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Energy, work, quantity of heat

C1 to C2 mult by Column 1 SI unit Column 2 non-SI unit C2 to C1 mult by
9.52 x 10-4 joule, J British thermal unit, btu 1.05 x 103
0.239 joule, J calorie, cal 4.19
107 joule, J erg 10-7
0.735 joule, J foot-pound 1.36
2.387 x 10-5 joule per square meter J m-3 calorie per square centimeter (langley) 4.19 x104
105 newton, N dyne 10-1
1.43 x 10-3 watt per square meter, W m-2 calorie per square centimeter minute (irradiance) cal cm-2 min-1 698

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Water measurements

C1 to C2 mult by Column 1 SI or sometimes accepted unit* Column 2 non-SI unit C2 to C1 mult by
9.73 x 10-3 cubic meter, m3 acre-inches, acre-in 102.8
9.81 x 10-3 cubic meter per hour m3h-1 cubic feet per second, ft3 s-1 101.9
4.40 cubic meter per hour m3h-1 US gallons per minite, gal min-1 0.227
8.11 hectare*-meters, ha-m acre-feet, acre-ft 0.123
97.28 hectare*-meters, ha-m acre-inches, acre-in 1.03 x 10-2
8.1 x 10-2 hectare*-centimeters, ha-cm acre feet, acre-ft 12.33
The hectare (ha, 103 m2) is not an SI unit, but is accepted by some journals.
It is also widely used in commerce.

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Electrical conductivity; plane angle

C1 to C2 mult by Column 1 SI unit Column 2 non-SI unit C2 to C1 mult by
10 siemens per meter
S m-1		 millimho per centimeter, mmho cm-1 0.1
57.3 radian, rad degrees (angle) 1.75 x 10-2

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Nutrients (elements & oxides)

C1 to C2 mult by Column 1
Pure Element		 Column 2 Oxide C2 to C1 mult by
2.29 P P2O5 0.437
1.20 K K2O 0.830
1.39 Ca CaO 0.715
1.66 Mg MgO 0.602

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