Center Pivot Irrigation Acre-Inch Calculator
Calculate acre-inches of water applied by a center pivot from flow rate, run time and irrigated area, for accurate irrigation scheduling.
How This Calculation Works
Acre-inches equals flow in gallons per minute times minutes of run time, divided by 27,154 gallons per acre-inch. A pivot pumping 800 gpm for 12 hours applies about 21 acre-inches across the field. Dividing by the irrigated acres gives the depth applied in inches.
Field Calibration & Rate Reference Chart
| Surface ac | Avg depth | Acre-feet | Copper lb @ 1 ppm |
|---|---|---|---|
| 0.25 | 4 ft | 1.0 | 2.7 |
| 0.5 | 4 ft | 2.0 | 5.4 |
| 0.5 | 6 ft | 3.0 | 8.2 |
| 1.0 | 4 ft | 4.0 | 10.9 |
| 1.0 | 6 ft | 6.0 | 16.3 |
| 1.5 | 5 ft | 7.5 | 20.4 |
| 2.0 | 5 ft | 10.0 | 27.2 |
| 2.0 | 8 ft | 16.0 | 43.5 |
| 3.0 | 6 ft | 18.0 | 49.0 |
| 5.0 | 6 ft | 30.0 | 81.6 |
Common Questions
How many gallons are in an acre-inch?
One acre-inch equals 27,154 gallons, the volume one inch deep over one acre. That figure converts flow and run time into applied depth. It is the standard unit for irrigation scheduling.
How do I calculate acre-inches from a center pivot?
Multiply flow in gallons per minute by the minutes of run time, then divide by 27,154. An 800 gpm pivot running 12 hours applies about 21 acre-inches. Divide by acres for the depth in inches.
How much water does a center pivot apply per pass?
A single pass typically applies a quarter to one inch, depending on the pivot's speed and nozzle package. Slower speeds apply more. Multiple passes build up the total seasonal depth.
How do I know how much to irrigate?
Match irrigation to crop water use, which you can estimate from evapotranspiration data or a soil-moisture check. Replace the water the crop uses without over-filling the root zone. Over-irrigation leaches nutrients and wastes water.