Sprinkler Coverage Calculator
A sprinkler wets a circle - but systems are built on squares of overlapping circles. Enter the nozzle's throw radius and flow to see the coverage math behind head-to-head design.
Inputs
Result
Planning estimate - not a substitute for a pressure-tested engineering design.
Formula
Full-circle area = π r². Head-to-head spacing = throw radius r. On a square grid, each head effectively serves r × r square feet, so application rate = 96.3 × GPM ÷ r².
Example
A head throwing 15 ft at 2.5 GPM: wetted circle ≈ 707 sq ft, but plan on 15 ft spacing and ~225 sq ft served per head, applying ~1.07 in/hr.
Assumptions
- Nozzle performs at rated radius (correct pressure, no wind).
- Square grid with head-to-head overlap; triangular grids cover slightly more area per head.
- Part-circle heads are counted as fractions of full-circle heads in real designs.
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
Overlap is not waste - it is what makes coverage uniform. A head alone wets a circle; a grid of overlapping circles wets the square between them almost evenly.
Next Step
Count the heads your area needs with the Sprinkler Head Calculator, then verify zone flow with the Sprinkler Zone Calculator.
Frequently Asked Questions
Why space heads at the throw radius, not the diameter?
Spacing at the radius gives each point on the grid water from several heads, evening out the naturally stronger pattern near the head.
Does wind change coverage?
Yes - wind stretches patterns and widens dry gaps. In windy sites, designers tighten spacing to 90% of radius or less.