Works out net and gross irrigation for any field and growth stage from FAO-56 crop coefficients, your ET₀, effective rainfall (or monthly totals via the FAO formula) and irrigation efficiency — in litres, m³ and acre-inches, with depth per irrigation.
Calculates crop evapotranspiration (ETc) for 30 crops at each growth stage from FAO-56 Kc values, with an optional dry or windy climate correction, rainfall and irrigation method — plus a Kc curve showing daily need by stage.
Sizes a drip storage tank from plant count, emitters per plant, dripper flow, run time, zones and buffer days, and checks the schedule against crop water use as a depth in mm/day. Crop presets fill in a peak-summer layout from FAO-56.
Adds livestock (OMAFRA rates by animal class, with a hot-weather option) and irrigation demand (Kc × ET₀ ÷ efficiency), with separate reserve days for animals and crops, to give total storage and a suggested tank size.
Calculates water used per session, week and year from heads, flow and run time, with water cost, depth applied, precipitation rate, pressure-corrected flow and the run time your lawn or crop actually needs.
Computes daily water needs and tank size by species and class (milking or dry cow, ewe with lambs, finisher pig, layer…) using OMAFRA rates, with temperature factors from NDSU's beef cattle table.
Builds total dynamic head from lift, outlet pressure, pipe friction and filter losses, then gives water and brake horsepower, the standard motor or engine size to buy, electrical input power and running cost.
Sizes a field irrigation tank from crop (FAO-56 Kc), peak ET₀, field area, irrigation efficiency, refill interval and buffer — and checks whether your borehole or source can keep up, with the largest area it can water.
Estimates daily, weekly and monthly greenhouse water use from growing area, crop, season and irrigation method — including drain-to-waste for substrate growing — with litres per plant and a storage tank size.
Water Planning Tools for Farmers, Growers & Agronomists
Agricultural water management sits at the intersection of productivity and sustainability. Too little water and yields collapse; too much and you waste a finite resource, raise input costs, and risk waterlogging or root disease. The nine tools in this category give smallholders, commercial growers, and irrigation engineers a single, reliable calculation layer — from seasonal crop water budgets built on the FAO-56 crop coefficient method, to right-sizing drip tanks, field storage, livestock water and greenhouse supply. Every tool shows its working, lists its sources, and was reviewed by John Mac, PE. Whether you're planning a new drip scheme in an arid region, scaling up a greenhouse operation, or working out how many kilolitres of on-farm storage will see your herd through a dry summer, every calculator here produces actionable numbers in plain language — no agronomy degree required.
How to Choose the Right Irrigation Calculator
1 Start with crop or livestock water demand
Before sizing any tank or pump, establish how much water your operation actually consumes. Use the Crop Water Need Calculator for field crops or the Livestock Water Requirement Calculator for animal operations. These outputs become the baseline inputs for every other tool in this category.
2 Match your delivery method to a sizing tool
Drip and sprinkler systems have very different tank and pump requirements. Use the Drip Irrigation Tank Size Calculator if you're running emitter-based systems, or the Sprinkler Water Usage Calculator for overhead coverage. For large open fields, the Field Irrigation Tank Sizing Calculator handles hectare-scale planning directly.
3 Size your pump to match delivery, not just demand
A tank that's large enough is useless if the pump can't move water fast enough to meet peak demand windows. After establishing your volume needs, run the Irrigation Pump Size Calculator to confirm the required flow rate and pressure head — factoring in pipe runs and elevation.
4 Plan for dry season buffer with farm storage
For operations relying on rainfall, bore water, or intermittent mains supply, the Farm Water Storage Calculator lets you set a buffer of days and calculates the total storage needed to ride out supply gaps — accounting for both irrigation and stock water simultaneously.
5 Use the comparison table below to narrow your choice
Each calculator is optimised for a specific scenario. The table below maps common farming situations to the most relevant tool.
| Your Situation | Best Calculator | Key Output |
|---|---|---|
| Sizing a new drip scheme | Drip Irrigation Tank Size | Tank capacity (litres) |
| Planning seasonal crop water | Crop Water Need + Irrigation Requirement | mm/day, L/season |
| Cattle or sheep water supply | Livestock Water Requirement | L/day per animal |
| Choosing pump for field irrigation | Irrigation Pump Size | kW / HP rating |
| Whole-farm storage planning | Farm Water Storage | Total kL required |
| Greenhouse growing operation | Greenhouse Water Usage | L/day & monthly |
| Overhead sprinkler audit | Sprinkler Water Usage | L/session, cost |
Pro tip: For mixed farms, use the Farm Water Storage Calculator for the whole-farm figure — it takes livestock counts and irrigated crop area together and lets you set a longer reserve for the animals than for irrigation. Animals can't go long without water; crops can ride out a short gap on soil moisture.
How These Calculators Are Built and Reviewed
Every calculator in this category uses published methods and shows its working, so you can check the numbers yourself:
- FAO Irrigation and Drainage Paper No. 56 — crop coefficients (Kc), ETc = Kc × ET₀ and typical ET₀ ranges. Used by the crop, irrigation, drip, field, farm and sprinkler tools.
- FAO Training Manual No. 3 and No. 4 — effective rainfall formula and typical irrigation efficiencies (90% drip, 75% sprinkler, 60% surface).
- OMAFRA Factsheet 23-023 and NDSU Extension AS1763 — livestock water by animal class and by temperature.
- K-State Research and Extension MF-1040 — pump horsepower formulas and conversions.
Frequently Asked Questions
Irrigation water requirements depend on your crop type, field area, evapotranspiration (ET) rate, soil type, and local rainfall. Our Irrigation Water Requirement Calculator lets you enter these factors and outputs the total daily and seasonal water volume needed, so you can size your tank, pump, and supply infrastructure accordingly. As a reference point, crop water use is Kc × ET₀: at full cover in a hot, dry summer (ET₀ around 6 mm/day) most field crops use about 5–7.5 mm/day, before irrigation losses are added.
Multiply daily drip use by the number of days the tank has to cover, then add about 15% for the water below the outlet. Use our Drip Irrigation Tank Size Calculator: enter plant count, emitters per plant, dripper flow and run time (or pick a crop preset), and your buffer days. It also checks that the schedule matches crop water use — for example, 1 acre of drip tomatoes at peak needs about 32,400 L a day, so 3 days of storage means a tank of about 115,000 L.
Livestock water requirements vary widely by species, body weight, ambient temperature, and production stage. Average figures from the Ontario agriculture ministry (OMAFRA) are about 115 L/day for a milking dairy cow (68–155 L, rising with milk yield), 55 L for a beef cow with calf, 32.5 L for a 1,000 lb horse, 10 L for a ewe with lambs, 9 L for a finisher pig and 0.25 L for a laying hen. Heat raises intake sharply: in NDSU's beef cattle table, intake at 90 °F is about 63% higher than at 70 °F. Our Livestock Water Requirement Calculator accounts for herd size and temperature to give you a precise daily and weekly volume for storage sizing.
Pump size depends on the required flow rate (litres per hour) and the total dynamic head — which includes elevation difference, pipe friction losses, and end-pressure at the emitters. Our Irrigation Pump Size Calculator builds the total head from lift, outlet pressure, pipe friction and filter losses, then gives the water and brake horsepower and the motor size to buy. The US extension formula is water horsepower = GPM × head in feet ÷ 3,960. For example, 1 acre of drip at 90 L/min against 47 m of head needs about 1.56 HP at the pump shaft with a 60% efficient pump, so a 2 HP motor.
Greenhouse water use follows sunlight most of all, and the cover cuts evaporative demand — a study in unheated plastic greenhouses in Almería measured it at 30–40% below outdoors. A full-grown greenhouse tomato uses about 1.4–1.9 L per plant on a sunny day (UF/IFAS), roughly 3.5–5.7 L/m²; leafy crops use much less. Our Greenhouse Water Usage Calculator combines crop, season and irrigation method, and counts drain-to-waste for substrate growing.
Using FAO's typical field application efficiencies — 90% for drip and 75% for sprinklers — a sprinkler system has to pump about 20% more water than drip to give the crop the same amount (0.90 ÷ 0.75 = 1.2), because of evaporation, wind drift and uneven coverage. However, sprinklers are better suited for germination, frost protection, and dense plantings like turf or grain crops. Use our Sprinkler Water Usage Calculator to estimate exact consumption for your system, then compare it against drip totals from our Drip Tank Calculator to make the most cost-effective choice for your crop type and climate.