Irrigation Calculator
Calculate water requirements and irrigation scheduling for optimal crop production
Irrigation Parameters
Corn/Maize
Field Crops - 600mm seasonEnter the total irrigated area
Drip - Surface (90% efficiency)
Surface drip irrigationNormal (×1)
Temperature 20-30°C, RH 50-70%Cost per cubic meter of water
Water Requirements & Cost
666,667 m³
Total Water Volume
$333333.33
Total Irrigation Cost
Water Requirements:
Base Need:
600 mm
Weather Adjusted:
600 mm
Gross Need:
667 mm
Irrigation Schedule:
Number of Irrigations:
6
Water per Irrigation:
111 mm
System Efficiency:
90%
Cost Analysis:
Cost per Hectare:
$3333.33/ha
Cost per mm:
$5.000/mm/ha
Volume per Hectare:
6667 m³/ha
Irrigation Calculator: Water Requirements, Scheduling & System Efficiency
Our Irrigation Calculator computes crop water demand using evapotranspiration (ET) data and crop coefficients (Kc), then calculates gross irrigation requirements accounting for your system's application efficiency. Use it to schedule irrigation events, size pumps and pipes, and estimate seasonal water costs.
Crop Water Requirements — Reference ET & Crop Coefficients
| Crop | Peak ET (in/day) | Kc (peak) | Root Depth (ft) | Season |
|---|---|---|---|---|
| Corn | 0.30–0.35 | 1.20 | 3–5 | 120–140 days |
| Soybeans | 0.22–0.26 | 1.15 | 3–4 | 90–120 days |
| Alfalfa | 0.30–0.40 | 1.05–1.20 | 6–8 | Perennial |
| Cotton | 0.20–0.25 | 1.20 | 3–5 | 150–180 days |
| Winter Wheat | 0.18–0.22 | 1.15 | 3–5 | 210–240 days |
| Potatoes | 0.20–0.28 | 1.15 | 1.5–2 | 90–120 days |
| Tomatoes | 0.20–0.30 | 1.15 | 2–3 | 110–150 days |
| Drip Efficiency | — | — | — | 90–95% efficiency |
| Sprinkler Efficiency | — | — | — | 75–85% efficiency |
| Flood/Furrow | — | — | — | 50–60% efficiency |
How to Use the Irrigation Calculator
- Get ET₀ data — obtain reference evapotranspiration from your local weather station, NOAA, or ET network (AZMET, CIMIS, etc.) in inches per day.
- Select your crop and growth stage — the calculator applies the correct crop coefficient (Kc) for your crop's current stage (initial, development, mid, late season).
- Enter field size — input area in acres or hectares. For drip systems, you can also enter the number of emitters and flow rate.
- Set irrigation system efficiency — drip 90–95%, center pivot 80–85%, flood furrow 50–60%. Gross irrigation = Net ET ÷ Efficiency.
- Calculate run time — enter your system's application rate (in/hr or gal/min) and the calculator determines required run time per irrigation event and pumping hours per season.
Example Calculations
Example 1 — Drip Irrigation for 5 Acres of Tomatoes
- ET₀ = 0.25 in/day, Kc (mid-season) = 1.15 → ETc = 0.25 × 1.15 = 0.29 in/day
- Drip efficiency = 90% → gross irrigation = 0.29 ÷ 0.90 = 0.32 in/day
- Daily water volume = 0.32 in × 5 acres × 27,154 gal/acre·in = 43,446 gal/day
- At 100 gal/min pump: run time = 43,446 ÷ 100 = 434 minutes = 7.2 hours/day
Example 2 — Center Pivot for 160 Acres of Corn (Peak Season)
- ETc = 0.30 × 1.20 = 0.36 in/day; efficiency = 82% → gross = 0.44 in/day
- Water needed = 0.44 × 160 acres × 27,154 = 1,909,606 gal/day ≈ 1,328 gal/min
- Seasonal water (90 days peak): 0.44 in/day × 90 × 160 acres = 6,336 acre-inches = 528 acre-feet
Frequently Asked Questions
What is evapotranspiration (ET) in irrigation planning?
Evapotranspiration (ET) is the combined water loss from soil evaporation and plant transpiration. ET₀ (reference ET) is calculated for a hypothetical well-watered grass surface using the Penman-Monteith equation from temperature, humidity, solar radiation, and wind speed. Crop ET (ETc) = ET₀ × Kc, where Kc is the dimensionless crop coefficient representing how the specific crop's water use compares to the reference. ET-based irrigation scheduling is the most efficient method — it replaces only the water actually used by the crop.
What is a crop coefficient (Kc)?
The crop coefficient (Kc) adjusts the reference ET₀ for the specific crop and its growth stage. Kc values (from FAO-56): Initial stage (germination/establishment): 0.3–0.5. Development: increases from initial to mid-season value. Mid-season (peak vegetative/reproduction): typically 1.0–1.2 for most crops. Late season (maturation): decreases to 0.5–0.9. Kc values greater than 1.0 mean the crop uses more water than the reference grass (e.g., corn at 1.20 during silking).
What is the difference between drip, sprinkler, and flood irrigation?
Drip (micro) irrigation: delivers water directly to the root zone through emitters at 0.5–2 gal/hr. Highest efficiency (90–95%), best for vegetables, orchards, vineyards, and water-scarce regions. Higher capital cost. Sprinkler (overhead): center pivots, solid-set, and traveling guns apply water over the crop canopy. Efficiency 75–85%. Versatile for large field crops. Flood/furrow: water flows down furrows or across basins by gravity. Lowest cost but least efficient (50–60%) due to runoff and deep percolation. Common in rice and some surface-irrigated crops in the western US.
How do I know when my crops need water?
ET-based scheduling is the most precise method — irrigate when cumulative ETc equals your soil's allowable depletion (usually 50–60% of plant available water). Soil moisture sensors (tensiometers, capacitance sensors, gypsum blocks) measure actual in-field water status. Visual indicators: wilting in the early morning (before 8 AM) signals severe stress. Leaf curl in corn indicates water deficit. For scheduling: irrigate before stress, not after; a single severe stress event during reproductive stages can reduce yield 15–30%.
What is irrigation efficiency and how do I improve it?
Irrigation efficiency = (water stored in root zone ÷ total water applied) × 100%. Losses occur from evaporation from the soil and canopy, runoff, and deep percolation below the root zone. To improve: 1) Switch from flood to drip or sprinkler where feasible. 2) Irrigate at night to reduce evaporation losses. 3) Use deficit irrigation during less sensitive growth stages. 4) Install soil moisture monitoring. 5) Calibrate and maintain emitters/nozzles. A 10% efficiency improvement on a 500-acre center pivot system can save 50+ acre-feet of water per season.
Related Tools
- Fertilizer Calculator — Match soil fertility to crop nutrient requirements
- Weather Unit Converter — Convert mm/day to in/day and other weather units
- Crop Yield Estimator — Estimate field-level yield from management inputs
- Water Usage Calculator — Track total water consumption and costs