Lawn Sprinkler Coverage Calculator
Planning a sprinkler system starts with two questions: how many heads cover the lawn, and how long to run them. The number of heads is the lawn area divided by the area each head covers at head-to-head spacing, rounded up with extras for edges. Run time is the depth of water you want to apply divided by the system's precipitation rate. This calculator does both. Enter your lawn area, the coverage per head, your system's precipitation rate, and a target watering depth to size the system and set the timer. All empirical figures are your own editable inputs taken from the nozzle chart or a catch-can test.
Sprinkler coverage formula
Heads needed = ceil(lawn area / coverage per head)
Run time (min) = (target depth / precipitation rate) * 60
Gallons per cycle = lawn area (sq ft) * target depth (in) * 0.623
(0.623 gallons covers 1 square foot to a depth of 1 inch)
The 0.623 factor converts square-foot inches to gallons: one cubic foot is 7.48 gallons, and one square foot one inch deep is one twelfth of a cubic foot. Use head-to-head spacing so coverage areas overlap for uniform watering.
Lawn watering context
- EPA WaterSense recommends head-to-head coverage so each head reaches the next for uniform application.
- Find coverage per head and precipitation rate on the manufacturer nozzle chart, or measure with catch cans.
- Round head counts up and add heads at corners, edges, and odd-shaped areas.
- Water deeply and less often to build deeper roots and cut evaporation losses.
- Split long run times into soak cycles on slopes and clay soils to prevent runoff.
Sprinkler coverage: frequently asked questions
How many sprinkler heads do I need for my lawn?
Divide the total lawn area by the area each head covers at its rated spacing. A rotor head covering a 25-foot radius covers a large arc, while a fixed spray head covering a 12-foot radius covers far less. Heads should overlap (head-to-head coverage), so always round up and add heads at edges and corners.
What is head-to-head coverage?
Head-to-head coverage means each sprinkler throws water all the way to the next head, so spacing equals the throw radius. This deliberate overlap compensates for the lower precipitation at the edge of each head's pattern and gives uniform watering. It is the spacing practice recommended by the EPA WaterSense program for efficient irrigation.
How long should I run my sprinklers?
Run time depends on how fast the system applies water (its precipitation rate in inches per hour) and the depth you want to apply. Run time in minutes equals target depth in inches divided by precipitation rate in inches per hour, times 60. Many lawns need roughly 1 inch of water per week from all sources combined.
What is a sprinkler's precipitation rate?
The precipitation rate is how many inches of water the system lays down per hour over the watered area. It is set by the head's flow and spacing. You can find it on the manufacturer's nozzle chart, or measure it with the catch-can method: place straight-sided cans on the lawn, run the system for a set time, then average the depths collected.
Why should I water deeply and less often?
EPA WaterSense advises watering deeply and infrequently to encourage deeper roots and reduce evaporation losses. Splitting a long cycle into shorter soak cycles also reduces runoff on slopes and clay soils. Always adjust for rainfall and skip watering after rain to avoid waste.
Official sources
- U.S. Environmental Protection Agency: WaterSense Landscaping Tips.
- U.S. Environmental Protection Agency: WaterSense Outdoor Water Use.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.