Size the flow (GPM) for each irrigation zone: zone area, head type, spacing or head count, and precipitation rate — then total system GPM and valve / pipe recommendations.
This calculator sizes the flow (gallons per minute) required for each irrigation zone and the overall system. It uses the standard landscape hydraulics relationship between precipitation rate, area, and flow:
GPM per zone = (Precip rate in/hr × Zone area ft²) / 96.3
Head count = zone area ÷ (head spacing × row spacing), rounded up to whole heads. If you enter an explicit head count it is used instead.
Spray heads typically space 10–20 ft with precip rates of 1.5–2.5 in/hr.
Rotor heads typically space 25–50 ft with precip rates of 0.3–0.6 in/hr (low matched-precip patterns).
Drip zones flow by drip-line length and emitter rate — enter the total drip-line GPM as the zone flow directly (head count = 0).
Size the pump / main line for the largest single-zone demand, not the sum of all zones, because only one zone runs at a time via valve staging.