How Many Rotors Per Zone? GPM & Pressure Calculation for 40 PSI, ¾" Supply

Sizing Rotor Zones: The Math Behind Head Count

With 40 PSI static pressure and ¾" supply pipe, you're limited to ~8–9 GPM total flow.

The Calculation

• ¾" pipe at 8 GPM = ~4.5 ft/sec velocity (acceptable).
• Each rotor with a 2.0 GPM nozzle uses 2 GPM.
• Max rotors = 8 GPM ÷ 2 GPM = 4 heads per zone.

Why Not More Heads with Smaller Nozzles?

Nozzles below 2.0 GPM (e.g., 1.5 GPM) produce poor distribution uniformity—large dry spots near the head, "donut" patterns. Coverage suffers.

Design Tips

• Use matched precipitation nozzles (all 2.0 GPM on a zone).
• Space heads at head-to-head coverage (radius = spacing).
• If you need more heads, add a zone or increase supply pipe to 1".

Quick Reference