About the Irrigation Water Calculator
Irrigation water needed for a crop, in millimetres, cubic metres and pumping hours.
Also known as: crop water requirement, irrigation calculator, water per hectare, pump hours calculator.
How to use this calculator
- Enter area, crop water requirement, effective rainfall, irrigation efficiency and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
m³ = (crop need − rainfall) ÷ efficiency × 10 × hectares
Worked example
Using the values pre-filled in the calculator above:
- Area = 10 hectares
- Crop water requirement = 500 mm per season
- Effective rainfall = 180 mm
- Irrigation efficiency = 75 %
- Pump rate = 50 m³/hour
- Water cost per m³ = 0.15
the calculator returns:
- Water needed: 42,667 m³
- Net irrigation depth: 320 mm
- Gross depth with losses: 426.7 mm
- Per hectare: 4,267 m³/ha