Sprinkler spacing: head-to-head coverage in practice
12 July 2026 · 8 min read
Intuition says to space sprinklers as far apart as possible — fewer heads, less trenching, lower cost. Every Hunter and Rain Bird design catalogue says the opposite, and says it in the same words: each sprinkler must throw all the way to the next sprinkler. Here is where that rule comes from and how to apply it.
Why the spray patterns have to overlap
A sprinkler does not water evenly. Most of the water lands in the first half of its radius, and at the very end of the throw precipitation falls close to zero — a droplet travelling 5 metres breaks up on the way. If you placed sprinklers so their radii merely touched, the strip between them would receive a fraction of what the rest of the lawn gets. That strip is exactly where the yellow patches appear in the first hot week.
Head-to-head spacing means the distance between sprinklers equals the throw radius. The weakening tail of one sprinkler's stream lands precisely where the next sprinkler waters hardest, so the two precipitation rates add up and even out. In practice designers will stretch spacing to roughly 110% of the radius in sheltered, wind-free sites — but never further.
Arcs: 90°, 180°, 360°
Head-to-head spacing produces one simple, repeatable layout pattern — the same one you will see on every professional plan:
- Lawn corners: sprinklers set to a 90° arc, aimed along the edges towards the middle.
- Edges: 180° sprinklers along each side, spaced at most one radius apart.
- Interior: full 360° heads — only where the lawn is wider than twice the throw of the edge sprinklers.
Intermediate arcs (45°, 135°, 270°) exist for awkward corners and curves, not for economising on heads. If a plain rectangular lawn comes out full of exotic arcs, that is a sign the spacing is wrong.
Matched precipitation — the nozzle-mixing trap
Every zone (a group of sprinklers opened by one valve) must have a matched precipitation rate — all its sprinklers applying water at a similar intensity in mm/h. Which means:
| Nozzle family | Typical rate | Can share a zone with… |
|---|---|---|
| Fixed spray nozzles | 35–45 mm/h | other fixed spray nozzles only |
| Rotary nozzles (MP Rotator, R-VAN) | 10–20 mm/h | the same rotary family |
| Geared rotors | 10–15 mm/h | rotors with matched nozzle sets |
| Drip line | depends on emitters | other drip line, nothing else |
Good nozzle series have matched precipitation built in: a nozzle set to 90° puts out a quarter of the water of a 360° nozzle, so every patch of lawn receives the same mm/h regardless of arc. The condition is that the whole zone comes from one nozzle family, running at the same pressure.
Radius reduction has limits
The screw on the nozzle shortens the throw, but catalogues cap that reduction at roughly 25% of the nominal figure. Throttling harder ruins the stream break-up and with it the uniformity. If a lawn needs a 3.2 m throw and the nozzle still reaches 5 m at full reduction, that is not "close enough" — it is the wrong nozzle. Pick a shorter-range series.
Worked example: a 12 × 8 m lawn
Rotary nozzles with a 4 m radius at head-to-head spacing: four 90° heads in the corners, one 180° head at the centre of each 8-metre side, two 180° heads along each 12-metre side (every 4 m) — and no 360° heads at all, because opposing 180° heads already cover the 8 m width. Ten sprinklers in total. It looks dense on paper; on a precipitation grid it is what leaves the lawn with no weak spots.
You can generate the same pattern automatically: draw your lawn in the IrriForge editor and head-to-head placement, arc selection and the matched-precipitation check all happen for you — with a coverage map that shows every dry patch immediately. The groundwork for the whole process is in the step-by-step design guide.