Calculate crop coefficient Kc, standard crop evapotranspiration ETc, or reference evapotranspiration ETo by crop, growth stage, and unit.

Use crop and reference ET for the same location and time period.

Standard, well-watered crop conditions. Lookup values are typical FAO estimates and need local adjustment; ETc is not an irrigation dose or a water-stress estimate.

Related Calculators

Crop Coefficient Formula

The following formula is used to calculate the crop coefficient for a given standard crop evapotranspiration and reference evapotranspiration.

Kc = ETc / ETo

Variables:

  • Kc is the crop coefficient
  • ETc is the standard crop evapotranspiration
  • ETo is the reference evapotranspiration

To calculate the crop coefficient, divide the standard crop evapotranspiration by the reference evapotranspiration.

What is a Crop Coefficient?

A crop coefficient (Kc) is a factor used in agricultural water management to estimate the water requirements of different crops. It is used in conjunction with reference evapotranspiration (ETo) to determine the standard crop evapotranspiration (ETc) of a specific crop. The crop coefficient varies depending on the type of crop, its growth stage, and local climatic conditions. By using the crop coefficient, farmers and agricultural planners can make more accurate decisions about irrigation scheduling, while accounting separately for effective rainfall, soil-water storage, irrigation efficiency and crop water stress.

How to Calculate Crop Coefficient?

The following steps outline how to calculate the Crop Coefficient.

  1. First, determine the standard crop evapotranspiration (ETc).
  2. Next, determine the reference evapotranspiration (ETo).
  3. Finally, calculate the crop coefficient using the formula Kc = ETc / ETo.
  4. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Standard Crop Evapotranspiration (ETc) = 5 mm/day

Reference Evapotranspiration (ETo) = 6 mm/day. Thus Kc = 5 / 6 ≈ 0.8333 (dimensionless).