How to Calculate Irrigation Water Needs
Crop water requirement (ETc) is the amount of water a crop needs, measured in mm/day. It depends on crop type, growth stage, and climate. Summer crops need 6-8 mm/day, winter crops 3-5 mm/day.
1 mm of water over 1 feddan (4200 m²) = 4.2 m³. So if ETc = 6 mm/day, one feddan needs 6 × 4.2 = 25.2 m³/day.
Irrigation system efficiency: Drip 90%, Sprinkler 75%, Flood 60%. To find actual water needed, divide ETc by efficiency. Example: Drip at 90% → 25.2 / 0.9 = 28 m³/day.
Irrigation interval: Drip 1-3 days, Sprinkler 3-5 days, Flood 7-14 days. Water per irrigation = daily need × interval days.
Example: Tomato in 2 feddans, drip irrigation, ETc = 6 mm/day, interval = 3 days. Water = (6 × 3 × 4.2 × 2) / 0.9 = 168 m³ per irrigation. Duration = 168 / 50 (flow rate) = 3.36 hours.
Use our Irrigation Water Calculator in the Agriculture category — it supports all area units, 3 irrigation systems, and calculates duration.