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Sprinkler Head Spacing and Count Calculator

Sprinkler head centres from the published radius at design pressure, derated for wind, and the heads a square or triangular grid needs for the zone.

  • Answers as you type
  • Every formula cited
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Imperial · sales tax
The throw the nozzle is rated for, at the pressure the zone will actually run at.

Read the radius from the row of the performance table matching your operating pressure, not from the top of the table. A nozzle throwing its catalogue maximum at a pressure your supply cannot hold is the single commonest reason a designed layout under-performs on the ground.

How far apart heads sit, expressed against the throw they are rated for.

One hundred percent is head-to-head: the throw from one head reaches the next, so every point is covered by at least two patterns. Manufacturers' charts permit a little more than that in calm conditions and require less in exposed ones, and they allow more for triangular grids than for square. Take the number from the chart for the nozzle and layout you have chosen.

The reduction applied for the wind the site sees at the hours you plan to irrigate.

Wind shortens the throw on the upwind side and distorts the pattern on the downwind one, and no adjustment at the head corrects it. What matters is the wind at the irrigation hour rather than the daily average, which is one reason night and dawn watering wins twice: less evaporation and a smaller derate.

The longer dimension of the rectangle being covered.

Heads are laid out along this dimension within each row. For an irregular area, take the bounding rectangle for a first count and then adjust by hand — an L-shaped lawn is two rectangles sharing a boundary, not one big one.

The shorter dimension of the rectangle being covered.

Rows of heads run across this dimension. Narrow strips and long verges rarely suit a grid at all — strip nozzles carry their own rates and belong on their own valve rather than hanging off a rotor zone.

Whether alternate rows are aligned or offset by half a spacing.

Triangular spacing overlaps patterns from three directions instead of two and produces better uniformity on open ground, which is why manufacturers permit a wider spacing percentage for it. Square is easier to set out along a boundary and is usually the honest choice on a small rectangle where the offset row would run out of lawn.

Heads needed for the zone

12 heads

Medium confidence

A rectangle-and-grid count, which is what a first layout needs. It assumes every head is the same nozzle at the same pressure — the moment arcs vary, the flow behind each arc has to vary with them or the corners drift out of step with the middle of the lawn.

Spacing between heads along each row
13.5 ft
Spacing between rows
13.5 ft
Heads on each row
4 heads
Rows across the zone
3 rows
Ground served by each head
84.5 ft²
Heads actually land at, along each row
13 ft
Rows actually land at, across the zone
13 ft
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • Spacing = published radius × spacing percentage × (1 − wind derate). Head-to-head coverage is spacing equal to the radius, so that every point on the ground lies within the pattern of at least two heads
  • Triangular row spacing = head spacing × √3⁄2, the row offset of an equilateral triangular grid; square row spacing equals the head spacing
  • RULE OF THUMB, stated as one: the spacing percentage and the wind derate are BOTH taken from the manufacturer's spacing chart for the nozzle in question. The defaults here are a starting point for a calm site, not a published allowance, and manufacturers permit a wider percentage for triangular layouts than for square ones

Inputs used

Published Radius at the Design Pressure
15 ft
Spacing as a Percentage of the Radius (%)
100
Wind Derate (%)
10
Zone Length
39 ft
Zone Width
26 ft
Grid Layout
Square — rows aligned, easier to set out against a boundary

Intermediate steps

Spacing between heads along each row
13.5 ft
Spacing between rows
13.5 ft
Heads on each row
4 heads
Rows across the zone
3 rows
Ground served by each head
84.5 ft²
Heads actually land at, along each row
13 ft
Rows actually land at, across the zone
13 ft
Final result12 heads

Confidence note: A rectangle-and-grid count, which is what a first layout needs. It assumes every head is the same nozzle at the same pressure — the moment arcs vary, the flow behind each arc has to vary with them or the corners drift out of step with the middle of the lawn.

What this calculation does not cover

  • Counts a grid on a rectangle. Curved boundaries, planting islands and re-entrant corners all need heads the grid does not know about.
  • Assumes a matched nozzle family: a half-circle head must discharge half the flow of a full-circle one to apply the same depth, and mismatched sets fail this quietly.
  • Does not check flow. The heads counted here still have to fit within the zone's available flow and the valve's capacity, which is a separate calculation.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

30 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Part of a bigger job

This trade is one line of a job takeoff. Run the whole job and every other trade comes back with it, off the same measurements.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations3
  1. Spacing = published radius × spacing percentage × (1 − wind derate). Head-to-head coverage is spacing equal to the radius, so that every point on the ground lies within the pattern of at least two heads
  2. Triangular row spacing = head spacing × √3⁄2, the row offset of an equilateral triangular grid; square row spacing equals the head spacing
  3. RULE OF THUMB, stated as one: the spacing percentage and the wind derate are BOTH taken from the manufacturer's spacing chart for the nozzle in question. The defaults here are a starting point for a calm site, not a published allowance, and manufacturers permit a wider percentage for triangular layouts than for square ones
Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Still deciding? Spray Irrigation vs Drip — the factors that actually differ, with no invented prices.

How to calculate sprinkler head spacing and count in 7 steps

  1. Published Radius at the Design PressureThe throw the nozzle is rated for, at the pressure the zone will actually run at.
  2. Spacing as a Percentage of the Radius (%)How far apart heads sit, expressed against the throw they are rated for.
  3. Wind Derate (%)The reduction applied for the wind the site sees at the hours you plan to irrigate.
  4. Zone LengthThe longer dimension of the rectangle being covered.
  5. Zone WidthThe shorter dimension of the rectangle being covered.
  6. Grid LayoutWhether alternate rows are aligned or offset by half a spacing.
  7. Heads needed for the zoneThe tool computes the heads needed for the zone from those figures and shows the formula, its sources, and a confidence rating alongside it.

Heads needed for the zone by published radius at the design pressure

Page defaults, not your figures above.

Published Radius at the Design PressureHeads needed for the zone (heads)
10 ft24
15 ft12
20 ft12
25 ft9
30 ft6

Frequently asked questions

Why does head-to-head coverage need heads a full radius apart rather than half?
Because the pattern from a single head is always heaviest close to it and thins toward the edge of its throw. Setting the next head at the edge of the first one's reach means the thin outer ring of one pattern lands on the thin outer ring of the other, and the two sum to something close to even. Spacing at half the radius would be a great deal of even coverage bought with twice the heads and twice the flow.
Is a triangular grid always better?
It gives better uniformity per head on open ground, which is why charts allow it a wider spacing. It is worse where the shape fights it: on a narrow strip or against a straight boundary, the offset rows waste throw off the edge and leave awkward slivers at the ends. Open lawns favour triangular, boundaries and rectangles favour square, and a great many real gardens end up with one of each on different valves.
Should the wind derate be applied to the percentage or separately?
Either, as long as it happens once. They are kept apart here because they come from different places: the spacing percentage is the nozzle manufacturer's, and the derate is yours, from the site. Keeping them separate also means you can see how much of a tight layout is chart and how much is exposure, which matters when someone later asks why there are so many heads.
The count includes heads on the boundary. Is that right?
Yes, and it is deliberate. Coverage has to reach the edge of the turf, so the outer row sits on the boundary with part-circle nozzles throwing inward. Setting the outer row a half spacing in from the edge saves heads and leaves a dry margin along every boundary, which is exactly where a lawn is most visible and most walked on.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.