Calculate the irrigated area, revolution time, and water application rate for your center pivot system. This tool helps you schedule irrigation, verify application uniformity, and ensure your system delivers the right amount of water.
Enter pivot length, end gun extension, speed setting, system flow rate, and the base hours per revolution at 100% speed. The calculator computes wetted radius, total acres, hours per revolution, and water application in inches per revolution.
Wetted Radius (ft) = Pivot Length + End Gun Extension
Total Area (acres) = π × Radius² ÷ 43,560
Hours per Revolution = Base Hours at 100% × (100 ÷ Speed Setting%)
Lower speed settings mean slower pivot movement and longer revolution times.
Application per Revolution (inches) = (GPM × 60 × Hours/Rev) ÷ (27,154 × Acres)
The constant 27,154 converts gallons to acre-inches: 1 acre-inch = 27,154 gallons (43,560 sq ft × 1/12 ft × 7.48 gal/cu ft).
Application Rate (in/hr) = Application per Revolution ÷ Hours per Revolution
A pivot 1,320 ft long with 100 ft end gun: Radius = 1,420 ft. Area = π × 1,420² ÷ 43,560 = π × 2,016,400 ÷ 43,560 = 145.4 acres.
At 100% speed (24 hrs/rev) with 1,000 GPM: Application = (1,000 × 60 × 24) ÷ (27,154 × 145.4) = 1,440,000 ÷ 3,947,352 = 0.365 inches/rev. Rate = 0.365 ÷ 24 = 0.015 in/hr.
1. Measure the pivot length from center point to the last span (not including end gun). 2. Enter the end gun throw distance. 3. Set the speed setting percentage from the pivot control panel. 4. Enter the system flow rate in GPM from the flow meter. 5. Enter the manufacturer's base hours per revolution at 100% speed (typically 24-48 hours). Click Calculate.
Center pivot irrigation is the most efficient method for large fields, with typical application efficiencies of 85-95%. Proper scheduling requires knowing both the application rate per revolution and the daily crop water use (ET). By matching pivot speed to crop needs, farmers avoid both under-watering (yield loss) and over-watering (wasted energy, nutrient leaching, and disease pressure). The 27,154 gallon/acre-inch constant is fundamental to all irrigation calculations.
Common mistakes: Forgetting the end gun extension — it can add 5-15% more area. Using the manufacturer's nominal flow instead of actual measured flow (pressure and wear reduce output). Assuming uniform application — center pivots apply more water near the center and less at the ends due to overlap patterns. Ignoring wheel track compaction in wet conditions, which can reduce yields in tracked areas.
✓ Expert Reviewed: This calculator and its content have been reviewed by agricultural experts. Formulas are based on standard extension service recommendations.