Every crop loses water to evapotranspiration (ET) — combined evaporation from soil and transpiration through the plant — at a rate that changes with weather and growth stage. This calculator estimates your crop's total seasonal water need using average daily ET and the length of the growing season, adjusted for your irrigation method's efficiency.
Total Water Requirement (mm) = Average Daily ET (mm/day) × Growing Season Length (days). Converted to volume: Total Volume = Field Area (m²) × Water Requirement (mm) ÷ System Efficiency.
| Season/Conditions | Typical Daily ET |
|---|---|
| Cool season (winter) | 2-3 mm/day |
| Moderate (spring/fall) | 4-5 mm/day |
| Hot season (summer) | 6-8 mm/day |
For a summer vegetable crop with a 90-day season at an average ET of 6 mm/day, grown via sprinkler irrigation at 75% efficiency, on a 1-hectare (10,000 m²) field: Total water requirement = 6 × 90 = 540 mm. Total volume = 10,000 × 540 ÷ 0.75 = 7.2 million liters for the full season — a figure that helps you plan tube well capacity or canal water allocation well before the growing season peaks.
ET combines water lost directly from soil evaporation and water lost through plant transpiration as it grows — together they represent the total water a crop and its surrounding soil surface consume, which is the basis for calculating irrigation needs.
Temperature, humidity, wind speed, and sunlight hours all drive evapotranspiration rates — hot, dry, windy conditions in summer can push ET two to three times higher than cool, humid winter conditions, even for the same crop.
Yes significantly — water demand is lowest at seedling stage, peaks during flowering and grain/fruit fill (the most water-sensitive stages for most crops), and declines again near maturity, so a single average ET figure is a simplification useful mainly for total-season planning.
Mulching reduces soil evaporation by 20-30%, deficit irrigation timed to avoid only the most water-sensitive growth stages can cut water use with minimal yield loss, and switching to more water-efficient irrigation methods reduces the effective volume needed to meet the same crop demand.