Irrigation Zone Calculator

Overview

Reserves 15% of available flow, divides usable GPM by per-head flow, then estimates zones from a head-type coverage assumption.

Assumptions

• Usable flow is available GPM × 0.85.
• Coverage per head is a planning reference, not a site layout.

Worked example

With 10 available GPM and 3 GPM rotors, usable flow is 8.5 GPM and floor(8.5 ÷ 3) = 2 heads per zone.

Common mistakes

• Using an unmeasured GPM value.
• Grouping sprays, rotors, and drip together.

Limitations

It does not calculate friction loss, valve hydraulics, or matched precipitation.

Safety and local requirements

Follow local backflow, electrical, and water-use requirements.

Sources

• EPA WaterSense — irrigation efficiency background