Sprinkler Coverage Calculator
Lawn area and spray radius to head count and total flow rate.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the Sprinkler Coverage Calculator
Sizing a sprinkler system correctly prevents dry spots, water waste, and soggy areas from over-lapping heads. Here is how to use this calculator:
- Enter your lawn area. Measure the total area you need to irrigate in square feet. For irregular shapes, break the lawn into rectangles, calculate each, and add them together.
- Enter the spray radius. This is the distance from the head to the furthest point of water spray. Most residential spray heads have a 10-15 ft radius. Rotor heads typically cover 15-45 ft. Check your head's spec sheet for the exact radius.
- Select the spray pattern. Full-circle heads are used in open areas away from edges. Half-circle heads go along straight edges like fences or walkways. Quarter-circle heads go in corners.
- Choose head type. Spray heads deliver water quickly at 1-2 GPM but cover smaller areas. Rotor heads deliver water more slowly at 2-4 GPM but cover larger areas and work better on slopes.
- Read your results. The calculator shows head count based on 50% overlap (the industry-standard "head-to-head" coverage rule), total system GPM, and the raw vs. effective coverage per head.
About the Sprinkler Coverage Calculator
The 50% overlap rule (also called "head-to-head coverage") is the industry standard for sprinkler layout. It means each head should reach the next head, so the spray radius equals the spacing between heads, not the diameter. At 50% overlap, the combined output from adjacent heads creates uniform moisture across the entire coverage area, eliminating dry spots that occur at the edges of individual spray circles.
The GPM result helps you size your water supply. Most residential zones should not exceed 10-15 GPM on a single zone, depending on your water meter size and pressure. If the total GPM exceeds your capacity, split the heads into multiple zones. This calculator gives head count for the entire area; your installer will divide them into zones based on your water pressure and supply capacity.
Frequently Asked Questions
How far apart should sprinkler heads be spaced?
Sprinkler heads should be spaced so each head's spray reaches the next head, a rule called "head-to-head coverage." For a head with a 12-foot spray radius, space heads 12 feet apart (not 24 feet, which is the diameter). This creates a 50% overlap between adjacent heads, which is the minimum needed for uniform coverage. Spacing heads at full diameter leaves dry spots between heads, especially on windy days.
What is the difference between spray heads and rotor heads?
Spray heads deliver a fixed fan of water at high precipitation rates (1-2 inches per hour), covering a set pattern of 10-15 feet. They work best on flat, smaller areas with well-draining soil. Rotor heads rotate slowly and deliver water at lower precipitation rates (0.4-1 inch per hour), covering 15-45 feet. Rotors are better for larger areas, slopes, and clay soils that need slow, deep watering. Never mix spray heads and rotors on the same irrigation zone, as their precipitation rates are too different to balance properly.
How many GPM does a typical home sprinkler system use?
Most residential sprinkler zones run at 8-15 GPM. A standard 3/4-inch water meter can supply 10-20 GPM, and most homes should keep each zone under 75% of the meter's rated capacity. Typical spray head zones run 4-8 heads at 1-2 GPM each, totaling 4-16 GPM. Rotor zones run 3-6 heads at 2-4 GPM each. If your calculated GPM exceeds your water supply capacity, divide your heads into multiple zones and run them sequentially rather than simultaneously.
How long should I run sprinklers to water my lawn?
Most lawns need 1 to 1.5 inches of water per week from rain and irrigation combined. Spray heads deliver roughly 1-2 inches per hour, so a 20-30 minute run time achieves the weekly target in one session. Rotor heads deliver water much more slowly at 0.4-1 inch per hour, so zones with rotors often need 45-60 minutes to deliver the same amount. Run a tuna can test: place an empty can in the spray zone and time how long it takes to collect an inch of water to calibrate your specific system.