Conversion Factors

Imperial to Metric units

Imperial unit Metric unit
1 inch (in.) 2.540 centimetres (cm)
1 foot (ft) (= 12 in.) 30.48 cm
1 yard (yd) (= 3 ft) 0.9144 metre (m)
1 square yard (sq yd) 0.8361 sq m
1 acre (= 4840 sq yd) 0.4047 hectare (ha)
1 ounce (oz) 28.35 grams (g)
1 pound (lb) 0.4536 kilogram (kg)
1 hundredweight (cwt) (=112 lb) 50.80 kg
1 unit (1% of a cwt) (=1.12 lb) 0.508 kg
1 ton (= 2240 lb) 1.016 metric tonnes (= 1016 kg)
1 pint 0.5682 litre (l)
1 gallon (gal) (= 8 pints) 4.546 litre
1 fluid ounce = 1/20 pint 0.02841 litre = 28.41 ml
1 cubic foot 28.32 litre
1 bushel 36.369 litre

Conversion Factors:

To convert Multiply by
oz/acre to g/ha 70.06
Ib/acre to kg/ha 1.121
cwt/acre to kg/ha 125.5
cwt/acre to tonnes/ha 0.1255
unit/acre to kg/ha 1.255
tons/acre to kg/ha 2511
tons/acre to tonnes/ha 2.511
gal/acre to litre/ha 11.23

Meteorological data:

To convert Multiply by
Temperature:
°F to °C subtract 32 and multiply by 0.5556
°C to °F multiply by 1.8 and add 32
Solar radiation (RAD):
J/cm2 to MJ/m2 0.01
MJ/m2 to W/m2 11.6
Wind measurements:
Knots to m/s 0.5144
From 10m to 2m height (see equation (1) below) 0.78
From 2m to 10m height (see equation (1) below) 1.28
Average daily windspeed (m/s) from total daily windrun (km in 24 hours) 0.011574
Total daily windrun (km in 24 hours) from average daily windspeed (m/s) 86.4
Beaufort wind scale number (B) to windspeed (m/s) at 10m 0.836 B3/2
Vapour pressure (VAP):
kPa to mb 10

Equations for wind measurements:

  • 1) Adjusting wind measurements for different heights of measurement:
    Vh/V10 = 0.233+0.656*log10 (h+4.75)
    where Vh = speed in knots at height h, V10 = speed at 10m and h = height in m (Met Office 1982).
  • 2) Converting the Beaufort scale wind speed:
    v = 0.836 B3/2 m/s
    Where v is the equivalent wind speed at 10 metres above the sea surface and B is Beaufort scale number.

Chemical components of fertilizers:

Oxide to element Multiply by
P2O5 to P 0.436
K2O to K 0.830
MgO to Mg 0.603
SO3 to S 0.400
CaCO3 to Ca 0.400

Epsom salts: A crystalline form of magnesium sulphate, MgSO4.7H2O.

Kieserite: A crystalline form of magnesium sulphate, MgSO4.H2O.

References:

  • Rothamsted (1974), "Conversion Factors", Yields of the Field Experiments, 1973, pp 406-407 DOI: 10.23637/ERADOC-1-98 (whole book).
  • Meteorological Office (1982) "Observer's Handbook, 4th Edition, Met.0.933
  • Meteorological data: Instrument Description
  • DEFRA (2010) "Fertilizer Manual (RB209)" 8th Edition. The Stationery Office, UK. https://ahdb.org.uk/rb209
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For further information and assistance, please contact the e-RA curators, Sarah Perryman and Margaret Glendining using the e-RA email address: era@rothamsted.ac.uk