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Generated on: July 20, 2026 at 09:33 PM

Sprinkler Coverage Calculator

Inputs

Throw radius5 m
Spray patternFull circle (360°)
Area to water150 m²

This is the bare coverage count, not a system design. Real sprinkler layouts use head-to-head overlap, matched nozzles, and zones sized to the available flow and pressure, all of which raise the number of heads. Use it as a starting estimate, not a final plan.

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Lifestyle

Sprinkler Coverage Calculator

Work out the area one sprinkler head covers from its throw radius and spray pattern, and the minimum number of heads to water a lawn or garden bed.

Inputs

≥ 0 m
≥ 0 m²

Results

Enter a value to see results.

Details

A head with a 5 m throw covers about ..., so watering 150 m² needs at least ... heads.

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Sprinkler Coverage

A sprinkler coverage calculator works out how much ground a single sprinkler head waters and how many heads it takes to cover a lawn or garden bed. Enter the head's throw radius and its spray pattern — a full circle in the open or part of a circle along an edge — together with the area to water, and it returns the coverage per head and the minimum number of heads. It helps when planning an irrigation zone or checking whether existing heads reach the whole lawn.

How coverage is calculated

A sprinkler head wets a circle, or a slice of one, with the throw radius as its radius. The area of a full circle is πr2\pi r^2; a part-circle pattern covers that fraction of it. The number of heads is the area to water divided by one head's coverage, rounded up:

a=πr2⋅kN=⌈Aa⌉\begin{aligned} a &= \pi r^2 \cdot k \\ N &= \left\lceil \dfrac{A}{a} \right\rceil \end{aligned}

where rr is the throw radius, kk the arc fraction (one for a full circle, and the matching fraction for a half, third, or quarter circle), aa the coverage per head, AA the area to water, and NN the number of heads.

Worked example

A full-circle head with a 5 m throw, watering a 150 m² lawn:

a=π×52×1=78.5 m2N=⌈15078.5⌉=⌈1.91⌉=2\begin{aligned} a &= \pi \times 5^2 \times 1 = 78.5\ \text{m}^2 \\ N &= \left\lceil \dfrac{150}{78.5} \right\rceil = \lceil 1.91 \rceil = 2 \end{aligned}

Two heads cover the area on paper. In practice you would use more, because this count assumes each head waters its full circle once with no overlap.

Why the real count is higher

Sprinklers apply far less water at the edge of their throw than near the head, so a layout that only just touched at the tips would leave dry rings between heads. Good design uses head-to-head spacing, where each head throws all the way to its neighbours and the spray overlaps, which evens out the application but roughly doubles the number of heads. Available flow and water pressure also cap how many heads can run on one zone. Treat this calculator's result as a floor, then design the layout and zones around it. For watering beds instead of lawns, drip is more efficient — see Drip Irrigation Run Time Calculator.

Frequently Asked Questions (FAQ)

How many sprinkler heads do I need?

Divide the area to water by the area one head covers, then round up. A full-circle head with a 5 m throw covers about 79 m², so a 150 m² lawn needs at least two heads on that basis. This is a minimum, though — well-designed systems space heads head-to-head so their spray overlaps, which means the real count is higher than the bare coverage division suggests.

What is the throw radius?

The throw radius, or throw distance, is how far a sprinkler head sprays from the head outward. It depends on the nozzle and on the water pressure at the head: too little pressure and the throw falls short, too much and the stream breaks into mist that drifts. Manufacturers publish a throw range for each nozzle at a given pressure, so use the figure for your nozzle and check your system pressure.

Why do sprinklers need overlap?

Sprinklers put down much less water near the edge of their throw than close to the head, so if heads only just touched at their tips the grass between them would stay dry. The fix is head-to-head spacing, where each head throws all the way to its neighbours, doubling up the coverage so the overlap evens out the application.

This is why a real layout uses more heads than the simple coverage division, and why this calculator reports a minimum rather than a final count.

Disclaimer

This is the bare coverage count, not a system design. Real sprinkler layouts use head-to-head overlap, matched nozzles, and zones sized to the available flow and pressure, all of which raise the number of heads. Use it as a starting estimate, not a final plan.

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