Irrigation Calculator — How Much Water Does My Field Need?
Calculate irrigation water needed per week based on crop water requirements and rainfall.
Acre-Inches
6.0
Gallons
162,924
Run Time (min)
203.7 min
Run Time (hr)
3.39 hr
Formula
**Irrigation Volume Formula**
Acre-Inches = Area (acres) × Net Water Need (inches)
Gallons Needed = Acre-Inches × 27,154
Run Time (min) = Gallons Needed ÷ Flow Rate (gpm)
1 acre-inch = 27,154 gallons
Worked Example
**Example:** 4 acres, 1.5" net need, 800 gpm pump
Acre-Inches = 4 × 1.5 = 6 | Gallons = 6 × 27,154 = **162,924**
Run Time = 162,924 ÷ 800 = **203.7 min (3.4 hr)**
Frequently Asked Questions
What is net water need?
Net water need is the amount of water your crop requires after subtracting effective rainfall (evapotranspiration minus usable precipitation).
How do I find my crop's ET?
Your state extension service or USDA NRCS publishes ET tables by crop, growth stage, and month. Peak field-crop ET is typically 0.2-0.35 inches/day.
What are typical pivot flow rates?
Center pivot systems typically run 400-1,000 gpm depending on nozzle package and system pressure.