How Many Sprinkler Heads Do I Need? Heads, Zones and Run Time
A sprinkler layout is a grid of heads, one throw apart. A lawn of 60 × 40 ft with 15 ft heads needs 20 heads, which use 24.0 gpm and need 2 zones on a 12 gpm supply. The sprinkler system calculator does it for your lawn.
Heads and zones for common lawns
With a 15 ft throw, a 2 gpm full-circle head and a 12 gpm supply:
| Lawn | Heads | Flow with all on | Zones |
|---|---|---|---|
| 30 × 30 ft | 9 | 8.0 gpm | 1 |
| 40 × 30 ft | 12 | 12.0 gpm | 1 |
| 50 × 40 ft | 20 | 24.0 gpm | 2 |
| 60 × 40 ft | 20 | 24.0 gpm | 2 |
| 80 × 50 ft | 35 | 48.0 gpm | 4 |
| 100 × 60 ft | 40 | 56.0 gpm | 5 |
Precipitation rate and run time
The rate for a head covering a square of its throw, and the minutes for an inch of water:
| Throw | Flow of the head | Precipitation rate | Minutes for 1 inch |
|---|---|---|---|
| 10 ft | 1 gpm | 0.96 in/hr | 62 min |
| 12 ft | 1.5 gpm | 1.00 in/hr | 60 min |
| 15 ft | 2 gpm | 0.86 in/hr | 70 min |
| 15 ft | 3 gpm | 1.28 in/hr | 47 min |
| 30 ft | 5 gpm | 0.53 in/hr | 112 min |
How the layout works
- Head to head. The heads are as far apart as they throw, so each head wets the next.
- Corners and edges. The heads on the corners and edges are quarter and half circles, so they use less water.
- Zones. A zone is the group of heads on one valve. The flow of each zone must stay under the flow of your supply.
- Matched rates. Keep one kind of head in a zone, so that the water falls evenly.
Before you buy
- Measure your flow and your pressure, and use the maker's chart for the nozzle to get the throw and the gpm.
- Draw the lawn to scale, and keep the water off the house, the paths and the road.
- Water early in the morning, in short cycles on a slope or on clay.
- Check the local rules on watering and on backflow prevention.
See also the lawn watering calculator and the sod calculator. These are estimates: a real layout needs a drawing.
Frequently asked questions
How many sprinkler heads do I need?
With head-to-head spacing the heads are one throw apart: a lawn of 60 × 40 ft and a 15 ft throw takes 20 heads.
How many zones do I need?
Add up the flow of all the heads and divide by the flow of your supply, rounded up. 24.0 gpm on a 12 gpm supply is 2 zones.
How do I measure my water flow?
Time how long it takes to fill a 5 gallon bucket from an outdoor tap and divide the gallons by the minutes. Use a figure a little under the result.
How long should I run the sprinklers?
The inches you want divided by the precipitation rate, times 60. At 0.86 in/hr, an inch a week takes 70 minutes, split into several cycles.
What is the precipitation rate?
The depth of water the heads put down in an hour. It is 96.25 times the gpm divided by the area one head covers in square feet.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.