Sprinkler / Irrigation Coverage Calculator
Work out roughly how many sprinkler heads a lawn area needs from your head's throw radius and spacing pattern. This covers head count for planning purposes — full system design should still account for water pressure and flow, covered in the FAQ below.
How this calculator works
Head-to-head spacing sets the coverage area assigned to each sprinkler head based on its throw radius and the layout pattern:
// square spacing (head-to-head = radius) coverage_per_head = spacing² heads_needed = ceil(area / coverage_per_head) // triangular spacing covers about 15% more area per head triangular coverage_per_head = spacing² / 0.866
A note on that triangular factor: circular spray patterns tile more efficiently in a staggered, triangular grid than in a square one, so each head effectively "owns" more usable lawn for the same head-to-head throw distance — about 15% more, which is why the triangular figure divides by 0.866 rather than multiplying by it. Either pattern still uses the same head-to-head rule: spacing equals the head's rated radius.
Worked example
A 100 ft × 80 ft lawn zone (8,000 sq ft), 20 ft head radius:
Square spacing:
- Coverage per head: 20² = 400 sq ft.
- Heads: ceil(8,000 ÷ 400) = 20 heads.
Triangular spacing:
- Coverage per head: 400 ÷ 0.866 ≈ 462 sq ft.
- Heads: ceil(8,000 ÷ 462) = 18 heads.
Same lawn, same head radius, but the triangular layout needs 2 fewer heads — a real, if modest, saving that grows with the size of the area.
Measuring your lawn
- Zones — add one entry per roughly rectangular section; irregular shapes are best broken into a few rectangles.
- Head radius — use your specific head's rated throw radius, not the maximum distance water visibly reaches, which is usually shorter under real pressure.
- Overlap — this is a head-count estimate, not a full layout; actual head placement still needs to account for lawn edges, obstacles and irregular shapes.
Frequently asked questions
What does "head-to-head spacing" mean and why does it matter?
It means each head's spray reaches the neighboring head's location, not just the edge of its own patch — that overlap prevents dry spots, since spray intensity tapers toward the edge of a head's throw.
Square vs triangular spacing — which is more efficient?
Triangular spacing tiles circular spray patterns more efficiently, covering roughly 15% more area per head than a square grid at the same head-to-head distance — at the cost of a slightly more complex layout to plan and install.
How do zones relate to water pressure and GPM?
Each zone is limited by available flow rate and pressure — too many heads on one zone can drop pressure below what each needs to spray properly. Splitting a large area into multiple sequential zones is standard; confirm the GPM math with a professional for anything beyond a simple system.