Agricultural Field Calculators
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Center Pivot Irrigation Calculator

Calculate gallons per acre, acre-inches applied, total water volume, and pivot revolution runtime for any center pivot system. Enter flow rate and pivot radius to find your application depth and scheduling parameters.

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Irrigation Water Usage

Calculate total water volume and runtime from depth, or applied depth from a known runtime.

Fill in the fields and press Calculate to see your results.

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Disclaimer — Irrigation calculations are estimates based on standard hydraulic formulas. Actual system performance depends on pump efficiency, pipe losses, field topography, and soil conditions. Consult a licensed irrigation engineer for system design.

Frequently Asked Questions

Acre-inches = (GPM × runtime hours × 60) ÷ (field acres × 27,154). MyFarmCalc calculates this automatically from your pivot radius, speed, and nozzle flow rate.
A pivot with a 1,320-foot radius covers approximately 125.7 acres (π × 1,320² ÷ 43,560). Corner areas add about 34 unirrigated acres per quarter section.
A common starting point is 8–10 GPM per acre for corn. A 125-acre pivot applying 1 inch per week needs approximately 1,000–1,250 GPM running continuously.
Acres = π × radius² ÷ 43,560. A 1,320-ft pivot covers ≈125.7 acres. A 2,640-ft (half-mile) pivot covers ≈502.7 acres.
Low-pressure drop nozzles at crop canopy: 90–95%. High-pressure impact heads: 70–80%. LEPA (Low Energy Precision Application) drag socks: up to 98%.
Injection rate (gal/min) = (gal/acre × pivot GPM) ÷ (acres × 60). For 3 gal/acre UAN on a 125-acre pivot at 1,000 GPM: 3 × 1,000 ÷ (125 × 60) = 0.4 gal/min.

Modern center pivot systems achieve 85–92% application efficiency — meaning 85–92% of applied water reaches the root zone. Older high-pressure impact sprinkler pivots may be 70–80% efficient. Low-energy precision application (LEPA) systems can reach 95%+ efficiency.

A typical quarter-section pivot (128 acres) applying 1 inch per week needs about 750–900 GPM from the well. Use the formula: GPM = (acres × inches/week × 18,857) ÷ (hours of operation per week). Most Columbia Basin pivots pump 700–1,200 GPM depending on acreage and desired application rate.