Penman-Monteith Evapotranspiration Calculator

Calculate reference evapotranspiration (ET₀) using the FAO-56 Penman-Monteith equation, the gold standard for irrigation scheduling and crop water requirement estimation.

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🌾 Agricultural Disclaimer: Results are estimates based on standard agronomic models. Local soil conditions, climate, variety selection, and management practices significantly affect actual outcomes. Consult local extension services and agronomists before making crop management decisions.
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Formula Definitions

The Penman-Monteith Evapotranspiration Calculator works by applying a well-defined formula to the values you enter. Understanding the formula behind the calculation helps you interpret the result and check that your inputs are correct. Below we break down the key components that drive the Penman-Monteith ET.

The core formula used by this calculator is:

Result = f(physical quantities, constants, conditions)

Each variable in the formula has a specific meaning:

  • physical quantities — Measured values with units entered into the Penman-Monteith ET.
  • constants — Physical or chemical constants (e.g. CODATA values, gas constant, Avogadro's number).
  • conditions — Temperature, pressure, concentration, or environmental state of the system.
  • Result — Computed physical or chemical quantity with associated units.

Note: Compare results with standard reference values or published experimental data.

How to Use This Calculator

  1. Enter the required values. Enter the required values into the Penman-Monteith Evapotranspiration Calculator input fields.
  2. Adjust settings. Adjust any settings, select applicable options, or choose units as needed.
  3. Calculate the result. Press Calculate to compute the result using the underlying formula.
  4. Interpret the output. Review and interpret your result using the provided context, reference ranges, or explanatory notes.

Glossary and Definitions

Physical quantity
A measurable property of a physical system, expressed as a numeric value with units.
Constant
A fixed, well-defined value (e.g. a CODATA constant) used across scientific calculations.
Significant figures
The digits in a measurement that carry meaning, reflecting the precision of the instrument.
Reference value
A published standard or experimental value used to validate a calculated result.
Evapotranspiration
A key concept referenced by the Penman-Monteith ET: Calculate reference evapotranspiration (ET₀) using the FAO-56 Penman-Monteith equation, the gold standard for irrigation scheduling and crop water requirement estimation.
Penman-Monteith
A key concept referenced by the Penman-Monteith ET: Calculate reference evapotranspiration (ET₀) using the FAO-56 Penman-Monteith equation, the gold standard for irrigation scheduling and crop water requirement estimation.
FAO-56
A key concept referenced by the Penman-Monteith ET: Calculate reference evapotranspiration (ET₀) using the FAO-56 Penman-Monteith equation, the gold standard for irrigation scheduling and crop water requirement estimation.
Crop water requirement
A key concept referenced by the Penman-Monteith ET: Calculate reference evapotranspiration (ET₀) using the FAO-56 Penman-Monteith equation, the gold standard for irrigation scheduling and crop water requirement estimation.

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Frequently Asked Questions