Sprinkler Spacing Calculator
Good coverage relies on 'head-to-head' spacing: adjacent sprinklers overlap so the weakest spray (at the edge of each head's throw) is topped up by its neighbour.
Enter Values
How to use this calculator
- Enter the length and width of the area you want to water, in metres.
- Enter the sprinkler's throw radius (the distance the spray reaches from the head) and, optionally, a head-to-head overlap percentage — 50% is the recommended default.
- Optionally add the flow rate of one head (L/min) to see the total flow the zone needs from your supply.
How it works
Good coverage relies on 'head-to-head' spacing: adjacent sprinklers overlap so the weakest spray (at the edge of each head's throw) is topped up by its neighbour. The recommended spacing is derived from the throw radius and the chosen overlap: spacing = throw radius × (1 − overlap% + 50%). At the default 50% overlap this simplifies to spacing equal to the throw radius, the classic irrigation rule where every head reaches the next head.
The calculator then lays out a square grid with a head at each edge of the area. Heads per row = ceil(width ÷ spacing) + 1 and the number of rows = ceil(length ÷ spacing) + 1, so the total head count is the product of the two. Multiplying the head count by the per-head flow gives the total flow the zone draws, which must not exceed what your tap, pump or mains can deliver at working pressure.
Worked example
20 m × 12 m lawn with 4 m throw pop-ups. Enter length 20 m, width 12 m, throw radius 4 m and leave overlap at the default 50% (head-to-head). Spacing = 4 × (1 − 50% + 50%) = 4.00 m. Sprinklers per row = ceil(12 ÷ 4) + 1 = 4; rows = ceil(20 ÷ 4) + 1 = 6; total = 4 × 6 = 24 heads. Adding a flow of 8 L/min per head gives a total flow of 192.0 L/min for the zone.
Common mistakes
- Confusing throw radius with throw diameter — enter the distance from the head to the edge of its spray (the radius), not the full width of the wetted circle.
- Spacing heads at the full throw radius with no overlap, which leaves dry rings and brown patches between heads; head-to-head (50% overlap) coverage is the industry standard.
- Ignoring supply limits — adding more heads raises the total flow, and if it exceeds your tap or pump capacity the pressure drops and every sprinkler's throw shrinks.
Frequently asked questions
What does head-to-head spacing mean?
It means each sprinkler is placed so its spray reaches the next sprinkler head. The edge of one head's throw is the weakest part of the pattern, so overlapping it with a neighbour's spray gives even coverage. This corresponds to the default 50% overlap, where the spacing equals the throw radius.
Should I use a square or triangular layout?
This calculator assumes a square grid, which is easiest to set out. A triangular (staggered) layout covers the same area with roughly 10–15% fewer heads because the circles nest more efficiently, but it is harder to mark out. For most home lawns a square grid is fine.
Why does my sprinkler's actual throw differ from the spec?
Throw radius depends on water pressure. If your supply pressure is below the head's rated pressure the spray falls short, so measure or test the real throw at your working pressure rather than using the box figure, and re-run the calculation.
Does this account for wind and slope?
No. Wind pushes spray downwind and slopes cause run-off, so reduce spacing (increase overlap) in exposed or sloping areas. This tool gives a still-air, flat-ground starting point that you then adjust on site.
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