// multi-utility computation suite · offline · instant · precise
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sci.crop-evapotranspiration-FAO56 Calculator
Calculates reference evapotranspiration ET₀ using the FAO-56 Penman-Monteith equation for a hypothetical grass reference surface with LAI = 2.88 and surface resistance 70 s/m. ET₀ ranges from < 1 mm/day in cold winter to > 8 mm/day in hot arid summer — it is the basis for all FAO irrigation scheduling.
Inputs
Tmax C
Thermal state of the substance. Check whether the formula needs Celsius, Fahrenheit, or Kelvin (K = °C + 273.15).
Tmin C
Thermal state of the substance. Check whether the formula needs Celsius, Fahrenheit, or Kelvin (K = °C + 273.15).
Rs Mj M2 D
Reference formula or conversion factor shown for context.
U2 M S
Rate of movement. 1 m/s = 3.6 km/h = 2.237 mph.
Rhmean Pct
Arithmetic average. Sensitive to outliers — if your data has extreme values, the median may be more representative.
Elev M
Reference formula or conversion factor shown for context.
Results
reference ET₀ (mm/day)
Sample size or count used in the calculation.
net radiation Rn (MJ/m²/day)
The value at the specified point or condition.
vapour pressure deficit VPD (kPa)
Reference formula or conversion factor shown for context.
psychrometric constant γ (kPa/°C)
Sample size or count used in the calculation.
saturation vapour pressure es (kPa)
How close the system is to its capacity limit. Above 80% sustained saturation typically leads to queuing and latency spikes.