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Conversion Factors Needed for Common Fertilizer Calculations



Authors as Published

Mark Reiter, Associate Professor and Extension Soils and Nutrient Management Specialist, Eastern Shore Agricultural Research and Extension Center, Virginia Tech


The world is a big place and farmers, industry, government, and others likely use different units, oxidation states, and measurements when calculating and reporting nutrient use for farming systems. The following table outlines some of the most common conversions needed for nutrient management. For instance, to convert K to K2O, you would multiply your K number by 1.2051. So, a fertilizer being reported as 49.8% K is also commonly reported as 49.8% × 1.2051 = 60% K2O. Therefore, you are equally correct to report muriate of potash (KCl) fertilizer as 49.8% K or 60% K2O, as long as you have the correct unit represented. However, note that fertilizer law generally states that certain oxidation states should be reported for certain nutrients (i.e. K2O must be used on Virginia fertilizer labels).

Table 1. Common fertilizer conversions needed for nutrient management calculations.

Column 1:
Multiply by Column 2: Multiplication Value
Nutrient Sources    
P to P2O5 Multiply P by 2.2910
P2O5 to P Multiply P2O5 by 0.4365
K to K2O Multiply K by 1.2051
K2O to K Multiply K2O by 0.8301
KCl to K Multiple KCl by 0.5244
KCl to Cl Multiply KCl by 0.4756
K2SOto K Multiply K2SO4 by 0.4487
Mg to MgO Multiply Mg by 1.6578
MgO to Mg Multiply MgO by 0.6032
MgCO3 to MgO Multiply MgCO3 by 0.4782
MgO to MgCO3 Multiply MgO by 2.0913
MgSO4 to Mg Multiply MgSO4 by 0.2020
MgCO3 to CaCO3 Multiply MgCO3 by 1.1867
CaO to Ca Multiply CaO by 0.7147
Ca to CaO Multiply Ca by 1.3992
CaCO3 to MgCO3 Multiply CaCO3 by 0.8426
CaCO3 to CaO Multiply CaCOby 0.5603
K2SO4 to S Multiply K2SOby 0.1840
CaSO4 to Ca Multiply CaSO4 by 0.2938
CaSO4 to S Multiply CaSO4 by 0.2350
SO4 to S Multiply SO4 by 0.3339
S to SO4 Multiply S by 2.9963
NaCl to Cl Multiply NaCl by 0.6066
N to NH3 Multiply N by 1.2158
N to KNO3 Multiply N by 7.2162
NH3 to N Multiply NH3 by 0.8225
N to (NH4)2SO4 Multiply N by 4.7160
(NH4)2SO4 to N Multiply (NH4)2SO4 by 0.2120
(NH4)2SO4 to S Multiply (NH4)2SO4 by 0.2427
N to NH4NO3 Multiply N by 2.8571
NH4NO3 to N Multiply NH4NO3 by 0.3500
Parts per million (ppm) to pounds per acre (lbs./acre) Multiply ppm by 2.0
Pounds per acre (lbs./acre) to parts per million (ppm) Multiply lbs./acre by 0.5
Percent to gram per kilogram Multiply percent by 10
Gram per kilogram to percent Multiply gram per kilogram by 0.1
Mile to kilometer Multiply mile by 1.609
Kilometer to mile Multiply kilometer by 0.621
Foot to meter Multiply foot by 0.304
Meter to foot Multiply meter by 3.28
Acre to hectare Multiply acre by 0.405
Hectare to acre Multiply hectare by 2.47
Square foot to square meter Multiply square foot by 0.0929
Square meter to square foot Multiply square meter by 10.76
Gallon to liter Multiply gallon by 3.78
Liter to gallon Multiply liter by 0.265
Quart to liter Multiply quart by 0.946
Liter to quart Multiply liter by 1.057
Pound to gram Multiply pound by 454
Gram to pound Multiply gram by 0.00220
Pound to kilogram Multiply pound by 0.454
Kilogram to pound Multiply kilogram by 2.205
U.S. ton to tonne Multiply U.S. ton by 0.907
Tonne to U.S. ton Multiply tonne by 1.102
Yield and Rate    
Pound per acre to kilogram per hectare Multiply pound per acre by 1.12
Kilogram per hectare to pound per acre Multiply kilogram per hectare to 0.893
Bushel per acre (bu/acre) for 60 lb. bushel to kilogram per hectare Multiply bu/acre by 67.19
Bushel per acre (bu/acre) for 56 lb. bushel to kilogram per hectare Multiply bu/acre by 62.71
Bushel per acre (bu/acre) for 48 lb. bushel to kilogram per hectare Multiply bu/acre by 53.75
Gallon per acre to liter per hectare Multiply gallon per acre by 9.35
Liter per hectare to gallon per acre Multiply liter per hectare by 0.107
Fahrenheit (°F) to Celsius (°C) Multiply Fahrenheit by 5/9 × (°F - 32)
Celsius (°C) to Fahrenheit (°F) Multiply Celsius by (9/5 × °C) + 32  


Alley, M.M. 2000. “Part VIII: Fertilizers.” Agronomy Handbook. Publication 424-100. Virginia Cooperative Extension, Blacksburg.

American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 2020. “Chapter 7: Units and Measurements.” Publications Handbook & Style Manuel. Madison, WI.


Funding for this work was provided in part by the Virginia Agricultural Experiment Station and the Hatch program of the National Institute of Food and Agriculture, US Department of Agriculture.

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Publication Date

April 29, 2020