Irrigation Water Calculator & Crop Water Need
Calculates crop water need
Get the total water your crop needs in m³ and litres, the gross to pump after drip/sprinkler/ flood losses, how many irrigations, and the water you'd save switching to drip.
Seasonal water need ≈ 450–650 mm
Plan to apply about 3,372 m³ (3,372,380 litres) of water across roughly 10 irrigations of ~50 mm each. Switching from flood to drip would cut this by about a third — drip runs at 90% efficiency vs 60% for flooding.
Next: schedule irrigations to the crop's critical stages (flowering/grain-fill matter most), and subtract real rainfall as the season goes. Don't over-irrigate — it wastes water and leaches nutrients.
Seasonal water needs are indicative (FAO/ICAR ranges); local ET and soil change the actual figure.
Irrigation water — key facts
- Key identity
- 1 mm over 1 ha = 10 m³ = 10,000 L
- Rice
- ~1,250 mm/season (very high)
- Wheat
- ~500 mm/season
- Flood efficiency
- ~60%
- Drip efficiency
- ~90% (saves ~⅓ water)
- Gross water
- = net ÷ efficiency
- Units
- m³ & litres · acre/ha/bigha
- Privacy
- Runs in your browser; nothing uploaded
How crop water requirement is calculated
Every crop has a seasonal water requirement in millimetres — the depth of water it transpires and evaporates from sowing to harvest. Because 1 mm of water spread over 1 m² is exactly 1 litre, multiplying the requirement by your field's area gives the litres (and cubic metres) the crop needs. Effective rainfall counts toward that, so you only irrigate the shortfall.
But not all pumped water reaches the roots: flood irrigation loses ~40% to runoff and seepage, sprinklers ~25%, and drip only ~10%. So the gross water you must supply = net need ÷ efficiency — which is why drip can cut your water bill by a third for the same crop. Dividing the requirement by your per-irrigation depth gives the number of irrigations to schedule.
Rice & sugarcane water needs
The thirstiest crops — rice ~1,250 mm and sugarcane ~2,000 mm a season. See the exact m³ for your field and how drip trims it.
Drip vs flood water saving
Compare methods instantly: drip at 90% efficiency versus flood at 60% typically saves about a third of the water pumped.
How many irrigations
Set your per-irrigation depth and the tool tells you how many irrigations the season needs.
Rainfall-adjusted irrigation
Enter effective rainfall and only the shortfall is charged to irrigation — useful for monsoon-fed crops.
Frequently Asked Questions
How do I calculate the water requirement of a crop?+
Take the crop's seasonal water need in millimetres, subtract effective rainfall, and multiply by the field area — because 1 mm of water over 1 m² is exactly 1 litre, 1 mm over a hectare is 10,000 litres (10 m³). This tool does it for your crop, area and irrigation method.
How much water does rice need per acre?+
Rice is thirsty — about 1,000–1,500 mm a season (≈1,250 mm typical). Over one hectare that's roughly 12,500 m³ delivered to the field, and more to pump after irrigation losses. Wheat by contrast needs about 500 mm.
What is the difference between net and gross irrigation water?+
Net is the water the crop actually needs at the field. Gross is what you must pump or divert, because some is lost to evaporation, runoff and seepage. Gross = net ÷ irrigation efficiency — about 60% for flood, 75% sprinkler and 90% drip.
How much water does drip irrigation save?+
Drip runs at about 90% efficiency versus 60% for flood irrigation, so it typically cuts the gross water you pump by roughly a third for the same crop — often 30–50% savings in practice, plus better yields and less weed growth. The tool shows your exact saving versus flood.
How does rainfall change the calculation?+
Effective rainfall counts toward the crop's water need, so you only have to irrigate the shortfall. Enter your expected effective rainfall and the tool subtracts it; if rain meets the full requirement, no irrigation water is needed.
How many irrigations does my crop need?+
Divide the irrigation requirement by the depth you apply each time (often ~50 mm for surface irrigation). For example, a 500 mm wheat crop at 50 mm per irrigation needs about 10 irrigations — fewer and deeper for heavy soils, more and lighter for sandy soils or drip.
What units does the calculator use?+
It reports water in cubic metres (m³) and litres, and accepts area in acre, hectare, bigha, guntha or square metres. 1 m³ = 1,000 litres; 1 mm over 1 hectare = 10 m³.
When is water most critical for crops?+
At the moisture-sensitive stages — typically flowering and grain/fruit filling. A water shortage then costs far more yield than the same shortage during early growth, so prioritise irrigation around those stages.
Does this account for soil type and evapotranspiration?+
It uses typical seasonal crop water requirements (which already reflect average evapotranspiration). Your exact need varies with local climate (ET₀), soil water-holding capacity and variety, so treat the figure as a strong planning estimate.
Can over-irrigation hurt my crop?+
Yes — too much water waterlogs roots, leaches nutrients below the root zone, raises disease and wastes pumping cost and energy. Matching water to the crop's need is as important as supplying enough.