Sprinkler Coverage Calculator
Calculate the coverage area and precipitation rate of your sprinkler heads. Enter the throw radius, arc angle, and flow rate to determine coverage area and how long to run each zone.
Understanding Precipitation Rate
Precipitation rate measures how fast a sprinkler applies water, expressed in inches per hour. It depends on the flow rate (GPM) and the area covered. A head with high GPM and small coverage area has a high precipitation rate, which can cause runoff on clay soils. Low precipitation rates apply water slowly, giving it time to soak in. When designing zones, match all heads on the same zone to similar precipitation rates. Mixing rotary and spray heads on one zone creates dry spots where rotary heads water and puddles where spray heads over-apply.
Head-to-Head Coverage Explained
The golden rule of irrigation design is head-to-head coverage: each sprinkler head should throw water all the way to the next head. If a head has a 30-foot radius, the next head should be no more than 30 feet away. This creates overlap that compensates for wind, low pressure, and the natural decrease in application at the outer edge of the spray pattern. Without proper overlap, you get donut-shaped dry rings between heads that become visible as brown patches during hot weather.
Frequently Asked Questions
What is a good precipitation rate?
Rotary heads typically deliver 0.4 to 0.8 inches per hour. Spray heads deliver 1.2 to 2.0 inches per hour. Match the rate to your soil type: sandy soil absorbs 1+ in/hr, clay absorbs only 0.2 in/hr.
How long should I run my sprinklers?
Run sprinklers long enough to apply 1 inch of water per session, typically once or twice per week. Divide 1 inch by your precipitation rate (in inches per hour) and multiply by 60 to get minutes.
What does arc angle mean?
The arc is the sweep angle of the sprinkler. Full circle (360°) waters in all directions. Half circle (180°) covers one side. Quarter circle (90°) handles corners. Most rotary heads have adjustable arcs.