Sprinkler Calculator
How fast does your sprinkler actually apply water? From head flow and spacing you get the application (precipitation) rate in inches per hour - the number that turns any watering target into a run time.
Inputs
Result
Planning estimate - not a substitute for a pressure-tested engineering design.
Formula
Application rate (in/hr) = 96.3 × head flow (GPM) ÷ area per head (sq ft). The constant 96.3 converts GPM spread over square feet into inches per hour.
Example
A 2.5 GPM head covering a 15 × 15 ft square: rate = 96.3 × 2.5 ÷ 225 ≈ 1.07 in/hr, so one inch of water takes about 56 minutes.
Assumptions
- Square, evenly spaced layout with head-to-head overlap.
- No wind distortion or pressure variation between heads.
- Flow is the nozzle's rated output at your operating pressure.
Limitations
This tool is a planning aid for DIY design and pre-design work. It does not replace an on-site pressure and flow test, a catch-cup uniformity test, or local code and backflow requirements. For steep slopes, long pipe runs, large elevation changes or commercial-scale systems, have a qualified irrigation designer verify the plan before installation.
What This Means
Typical spray zones apply 1.5-2 in/hr while rotary zones apply 0.4-0.8 in/hr. Slower rates let soil absorb water with less runoff - that is why rotaries run longer per session.
Next Step
Turn the rate into a weekly schedule with the Sprinkler Run Time Calculator, or size the zone these heads belong to with the Sprinkler Zone Calculator.
Related Guides
Sources
Frequently Asked Questions
What is precipitation rate in irrigation?
It is how fast sprinklers apply water, in inches per hour - the same idea as rainfall intensity, which is why schedules are built from it.
Why do rotary zones need longer run times than spray zones?
Rotaries apply water more slowly (lower precipitation rate), so the same inch of water takes more minutes.