Sprinkler Head Spacing Calculator

The spacing rests on one design identity: head-to-head (100% overlap) means heads sit one radius apart. A sprinkler throws the least water at the edge of its arc, so the next head must reach the previous one to avoid dry rings (Irrigation Tutorials). The overlap-target percent maps onto that identity:

spacing = radius × (2 − overlapPct / 100)
  overlapPct 100 → radius × 1.0  = radius      (head-to-head)
  overlapPct  50 → radius × 1.5                (budget)
  overlapPct   0 → radius × 2.0  = diameter    (edges just touch)

row spacing (square)     = spacing
row spacing (triangular) = spacing × 0.866     (≈ √3/2)

heads/row = ceil(length / spacing) + 1         (+1 closes the far edge)
rows      = ceil(width / rowSpacing) + 1
total     = heads/row × rows

zone flow   = total × GPM/head
zones       = ceil(zone flow / max GPM per zone)   (default 12)

Worked example (square): radius 20 ft, head-to-head, 80 × 60 ft area, 3.0 GPM/head → 20.0 ft spacing, 5 × 4 = 20 heads, 60 GPM → 5 zones. Switch to triangular and the tighter rows (17.32 ft) raise the count to 25 heads.

Three advisory checks never block the result: the diameter × 0.6 maximum (spacing > radius × 1.2 risks dry spots), a wind derate that tightens spacing to 45% of diameter when wind tops 10 mph, and Stryker's Rule for rotors (spacing in feet should not exceed inlet psi). Counts always round up — under-counting leaves uncovered area.

Spacing decides coverage; the controller decides how long that coverage runs, which is what the zone runtime calculator works out from precipitation rate. Contractors billing the work rather than planning their own yard will want what to charge for a spring startup or a head and zone repair, and in Texas the license question comes first: who may install or repair an irrigation system there is regulated by the state.