Rice Water Requirement Calculator
Work out the seasonal and per-irrigation water requirement of rice (paddy) (FAO-56 ETc = ET₀ × Kc, peak Kc 1.2) for your field, climate, soil and irrigation method.
This is the crop's evapotranspiration; transplanted lowland paddy needs much more once puddling, percolation and 5 cm standing water are added. Alternate wetting and drying (AWD) can cut total water 15–30% with no yield loss.
Indicative planning figures based on published research averages. Local soil tests, varieties and weather change actual requirements — confirm with your agronomist or extension officer.
Disclaimer: This tool is for general informational and estimation purposes only and is not professional financial, tax, accounting or legal advice. All figures are estimates — verify with a qualified professional before making decisions. Read the full disclaimer.
Farmers and irrigation planners use the free Rice Water Requirement Calculator to turn the FAO-56 crop coefficients for rice (paddy) into a real seasonal water volume and an irrigation interval for their own field — no agronomy tables, works offline.
About Rice Water Requirement Calculator
Lowland paddy is the thirstiest field crop — 1000–1500 mm including the puddling and standing-water needs that this ET-based figure does not add. This calculator uses the FAO-56 method — crop evapotranspiration ETc = ET₀ × Kc — with rice (paddy)'s own crop coefficients (Kc 1.05 initial, 1.2 mid-season, 0.9 late) across a 130-day season. Pick your climate band (which sets reference ET₀), irrigation method (drip, sprinkler, pivot or surface — each with its own efficiency) and soil texture, and it returns the seasonal water need in cubic metres, the peak daily demand, the net depth per irrigation and how many days to wait between irrigations.
How to use Rice Water Requirement Calculator
- 1Enter your field area and choose the climate band matching your season.
- 2Select your irrigation method and soil texture.
- 3Read the seasonal water volume, peak daily demand and irrigation interval, then follow the scheduling note.
Why use Rice Water Requirement Calculator?
- ✓Uses rice (paddy)'s real FAO-56 Kc curve, not a flat factor
- ✓Accounts for drip / sprinkler / pivot / surface efficiency
- ✓Gives seasonal volume, peak daily need and an irrigation interval
- ✓Free, instant and fully in-browser — works offline in the field
Frequently asked questions
How much water does rice (paddy) need?+
Lowland paddy is the thirstiest field crop — 1000–1500 mm including the puddling and standing-water needs that this ET-based figure does not add. The exact figure depends on climate and season length; this tool sums ET₀ × Kc across the crop's 130-day growth stages for your conditions.
Why does rice need so much water?+
Most 'rice water' is not transpiration but percolation and seepage from continuously flooded fields plus the puddling water. The ET component shown here is modest; the field total of 1000–1500 mm comes from keeping the field ponded.
Can I save water in rice without losing yield?+
Yes — alternate wetting and drying (AWD), where the field is allowed to dry to ~15 cm below surface before re-flooding, typically saves 15–30% of water with no yield penalty on suitable soils.
What is ET₀ and Kc?+
ET₀ (reference evapotranspiration) is how fast a standard grass surface loses water in your climate. Kc (crop coefficient) scales it to a specific crop and growth stage. Crop water use ETc = ET₀ × Kc — the basis of FAO-56 irrigation scheduling.
Is this calculator free and private?+
Yes — free, no sign-up, and all calculation runs in your browser, so it works offline in the field and your data never leaves the device.
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