Pivot Irrigation Calculator

Center pivot systems irrigate a circle, not a square, so this calculator's core job is converting a linear pivot length into circular area using A = πr², then layering the end-gun's extra throw radius on top as its own ring of additional coverage. From there it works out application depth per revolution: total gallons pumped during one full rotation (system flow × revolution time), converted from gallons to cubic inches and divided by the wetted area in square inches, giving inches of water depth actually laid down. This is the number growers care about most — it tells you how much water the crop receives each time the pivot completes a lap.

Dividing that depth by the revolution time (scaled to a 24-hour day) gives the system's daily application capacity, which the calculator compares against your peak crop ET demand adjusted for application efficiency to flag whether the system can physically keep up during the hottest, highest-demand part of the season — a pivot that takes 96 hours per revolution may simply be too slow for a crop needing 0.3+ inches per day at peak. GPM per acre is reported as a quick capacity benchmark; most systems target 4-6 GPM per acre, and much lower numbers usually mean an undersized well or pump relative to the area being covered. One nuance worth flagging: this application-depth math assumes uniform water distribution across the wetted circle, when real pivots always show some falloff toward the outer towers and at the end-gun's edge — actual on-ground uniformity depends on nozzle package and pressure regulation that this calculator doesn't model directly.