Irrigation Water Calculator

Estimate the water a field or garden needs and how long to run the pump.

Area	1 acres or ha
Unit	Acres
Water to apply	50 mm
System efficiency	75 %
Pump or supply flow	300 L/min

Area

acres or ha

Unit

Water to apply

Crop water need minus effective rain; e.g. 5 mm/day × 10 days.

System efficiency

Flood 50–60%, sprinkler 70–80%, drip 85–95%.

Pump or supply flow

L/min

Water needed

269.8 m³ (269,790 L)

Run the pump about 14 h 59 min at 300 L/min. That's 71,271 US gallons.

Where the water goes at 75% efficiency

Reaches the crop75%: 202.3 m³
Lost (evaporation, runoff, leaks)25%: 67.4 m³

About the Irrigation Water Calculator

Enter the area, the depth of water to apply, the irrigation efficiency and the pump flow. The calculator gives the water needed and how long to run the pump.

1 mm of water over 1 m² is 1 litre, so 1 mm over a hectare is 10,000 L and over an acre about 4,047 L. Divide by the irrigation system's efficiency to account for evaporation, runoff and deep drainage. Crop water needs come from evapotranspiration (ET) data, often 3–8 mm/day in the growing season.

The formula

Litres = area (m²) × depth (mm) ÷ efficiency

Worked example

1 acre, 50 mm of water, 75% efficiency, a 300 L/min pump

4,047 m² × 50 mm = 202.3 m³
÷ 0.75 = 269.8 m³ (269,790 L)
About 14 h 59 min of pumping

Questions people ask

How do I know how much to apply?

Use crop ET × days since the last irrigation, minus effective rainfall, or a soil moisture sensor.

How do I measure pump flow?

Time how long it takes to fill a container of known volume.