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.