Sprinkler Coverage Calculator
How many sprinkler heads cover a lawn at head-to-head spacing, their precipitation rate, and how long to run the zone.
Result
Enter area to water to see the result.
https://calcgallery.com/landscaping/sprinkler-coverage-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use the Sprinkler Coverage Calculator
- Enter the lawn area, as one or more rectangles, and the throw radius and flow of your heads from the nozzle chart.
- Choose a square or triangular layout.
- Read the heads needed and the precipitation rate. Add the depth of water you want to apply to get the run time.
Where 96.25 comes from
A gallon is 231 cubic inches. One gallon a minute spread over one square foot (144 square inches) for an hour is
231 × 60 ÷ 144 = 96.25 inches per hourprecipitation rate (in/h) = 96.25 × total gpm ÷ area (ft²)precipitation rate (mm/h) = 60 × total L/min ÷ area (m²)run time = depth ÷ precipitation rateMany references round the factor to 96.3; the page uses the exact figure.
Square or triangular
With heads a radius apart, a square layout gives each head a square of the radius on a side to water. A triangular layout, rows offset like bricks, covers the gaps between circles better, so the water goes down more evenly. Each head then covers a smaller area, 0.866 of a square, so a triangular zone needs a few more heads.
With your numbers
- Spacing = radius; precipitation rate = 96.25 × total gpm ÷ area in ft²
Quick reference
Head counts round up; flows come from your nozzle chart.
| Job | Heads needed |
|---|---|
| 40 × 30 ft, 15 ft radius, square | 6 |
| 40 × 30 ft, 15 ft radius, triangular | 7 |
| 50 × 50 ft, 20 ft radius, square | 7 |
| 20 × 10 ft, 8 ft sprays | 4 |
| 12 × 9 m, 4.5 m radius | 7 |
| Two areas, 30 × 20 and 15 × 10 ft | 4 |
Common questions about the Sprinkler Coverage Calculator
- How many sprinkler heads do I need?
- 7 heads for a 40 by 30 foot lawn with a 15-foot throw in a triangular layout. Each head covers 15 × 15 × √3 ÷ 2 = 194.86 square feet, and 1,200 ÷ 194.86 = 6.2, rounded up to 7. A square layout gives each head 225 square feet, so the same lawn takes 6.
- How far apart should sprinkler heads be?
- One radius apart, head to head: each head throws water all the way to its neighbours. A 15-foot head is spaced 15 feet from the next, not 30. It looks like wasteful double coverage, but a sprinkler puts down much less water near the edge of its throw than close in, and only the overlap makes the watering even. Spacing at the diameter leaves dry rings.
- What is precipitation rate?
- How fast a zone puts water down, in inches or millimetres per hour: the total flow of its heads spread over the area. It tells you how long to run the zone to apply a given depth. Six heads at 2.6 gallons a minute over 1,200 square feet give about 1.25 inches an hour, so half an inch takes about 24 minutes.
- Can I mix spray heads and rotors in one zone?
- It is best not to. Sprays apply water several times faster than rotors, so a zone with both overwaters near the sprays by the time the rotors have done their part. Put each type on its own zone.
- How much should I water?
- That depends on the soil, the grass, the season and the weather, so the page supplies no figure. Enter the depth you want to apply and it gives the run time.