Irrigation Runtime Calculator

Overview

Divides target water depth by entered precipitation rate to estimate runtime, then flags cycle-and-soak where soil intake is low.

Assumptions

• Precipitation rate comes from the nozzle chart or field test.
• Target depth is an irrigation goal, not a universal weekly requirement.

Worked example

At 0.4 in/hr, applying 0.5 in takes 0.5 ÷ 0.4 × 60 = 75 minutes before any cycle-and-soak split.

Common mistakes

• Using a nozzle’s flow rate as precipitation rate.
• Programming one long cycle on clay without observing runoff.

Limitations

Rainfall, root depth, slope, weather, and distribution uniformity are not included.

Safety and local requirements

Observe local watering restrictions and avoid watering onto sidewalks or streets.

Sources

• EPA — Soak Up the Rain
• EPA WaterSense — irrigation efficiency background