Sprinkler calculator
A sprinkler waters a circle, but lawns are covered in squares — the effective area of each sprinkler is the square that fits inside its circle. The calculator uses that to give a minimum count.
Your measurements
Result
- Area covered by one sprinkler
- 32 m²
- Sprinklers needed (minimum)
- 4 pcs
A minimum for a regular lawn. Installers usually space sprinklers head to head, which can double the count.
How the calculation works
- Area covered by one sprinkler = 2 × radius² (the square inscribed in the watered circle).
- Sprinklers = lawn area ÷ area per sprinkler, rounded up.
Worked example
With a 4 m radius each sprinkler effectively covers 2 × 4 × 4 = 32 m². A 100 m² lawn needs 100 ÷ 32 = 3.1, so 4 sprinklers.
What the calculator assumes
- The radius is from the sprinkler's data sheet at your system's working pressure.
- The calculation is for a regularly shaped lawn.
When to adjust the result
- Installers usually space sprinklers head to head (each reaches its neighbour) for even watering — that can double the count. The result here is a minimum.
- Sprinklers are grouped into zones according to the flow available at the tap; beds and hedges are better watered by drip.
Designing an even sprinkler layout
For even watering, sprinklers should spray to each other — head-to-head coverage — so the spacing roughly equals the throw radius. Spacing them further apart leaves dry rings between heads, which is the most common mistake.
Check how much water your supply can deliver (fill a bucket and time it) before choosing the number of heads per zone: a zone should never need more flow than the supply gives. Rotors and spray heads apply water at very different rates, so do not mix them in one zone. Water early in the morning to reduce evaporation and leaf disease.
Frequently asked questions
How many sprinklers do I need?
Lawn area divided by 2 × radius² as a minimum; head-to-head spacing needs more.
What is head-to-head spacing?
Placing sprinklers so each one throws water as far as the next sprinkler, which gives even coverage.
How many sprinklers per zone?
As many as your supply's flow rate allows at the required pressure. Add up each head's flow and keep the total below what you measured at the tap.
How long should I water a lawn?
Enough to give roughly 20–25 mm a week in dry weather, in one or two deep sessions rather than daily light ones; measure with a few cups on the lawn.