Irrigation Water Calculator & Crop Water Need
Calculates crop water need
“Real reviews from real users decide this tool's public rating.
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.
Enter your field & method
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.
Related farming tools
1900+ free tools, zero sign-up
Calculators, developer & SEO utilities, data, content, hardware and farming — all instant, private and in your browser.
Instant Results
Lumber, framing, and trim calculation tools for professional woodworking
Open FarmingMilk Urea Nitrogen (MUN) Feeding Balance Calculator
Free milk urea nitrogen (MUN) calculator. Read your herd's bulk-tank MUN against milk-protein % to diagnose wh
Open Dev & SEOnpm Dependency Analysis Fundamentals
MD5, SHA-256, SHA-512, SHA-3, BLAKE2, HMAC, PBKDF2, file hashing, verify, compare & free API — all in your bro
Open NicheCorporate Carbon Footprint Calculator 2026
Calculate full Scope 1, Scope 2 and Scope 3 corporate emissions with a stacked stream Sankey, SBTi 4.2% pathwa
Open ContentDesign Token Generator
Turn brand colors into a complete color token system — OKLCH 50–950 scales per role plus light & dark semantic
Open HardwareHardware Specifications Explorer
Faceted CPU & GPU specification explorer: filter by type, brand, process node, release year and TDP, then read
Open ProductivityPassword Tools
Test password strength against real standards (NIST 800-63B, OWASP ASVS), check against known breaches via k-a
Open ProLLM VRAM & Speed Estimator
Interactive LLM estimator: drag sliders for parameters, quantization, context, batch size, memory bandwidth, V
Open CalculatorAcreage
Open FarmingPasture Budget Calculator
Free pasture budget calculator. Enter pasture cover, residual, paddock area, herd size and intake to get how m
Open Dev & SEOIs Your JavaScript Bundle Too Big?
Drop a JS/CSS bundle or paste a webpack/Next.js stats.json and get the real gzip and Brotli size, an interacti
Open NicheData Center Carbon Footprint Calculator 2026
Compute hyperscale, colocation and enterprise data centre annual tCO2e from IT load, PUE and grid emission fac
Open ContentCSS Gradient Generator
Build production-ready CSS gradients — linear, radial and conic — with unlimited color stops and any angle, a
Open HardwareCPU & GPU Tier List Pro
The hardware hierarchy measured five ways: 130+ CPUs & GPUs (2015–2025) ranked into live S–D tiers by performa
Open ProductivityPassword Strength Tester
Open ProLocal LLM Hardware & Model Directory
Browse every GPU, model and best-of guide in the Local AI Advisor: what each graphics card can run, hardware r
Open CalculatorAsphalt Calculator Results
Open FarmingPiggery Profit Calculator
Free piggery profit calculator. Enter sows, litters a year, piglets per litter, mortality, market weight, pric
Open Dev & SEOWhere Are the Import Cycles in My Code?
Paste your import/require statements, a madge JSON, a DOT graph or an edge list and instantly find every circu
Open NicheFleet Emissions Calculator
Quantify your fleet's annual tCO2e by vehicle type with an animated convoy and per-vehicle emission trails. Se
Open ContentImage Color Extractor
Extract a ranked palette of dominant and accent colors from any image, logo or screenshot, with coverage perce
Open HardwareSilicon Architecture Explorer
Explore CPU and GPU silicon: group every part by microarchitecture (Zen, Ada Lovelace, RDNA, Ampere, Blackwell
Open Pro