Sprinkler Head Count and Spacing (NFPA 13)

How many sprinkler heads a room needs, how far apart, and how far off the walls.

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Example

You enter

Room length (ft) 40
Room width (ft) 30
Max protection area per head (ft²) 130
Max spacing between heads (ft) 15

You get

Governing spacing 11.40 ft
Heads per line 4
Num lines 3
Total heads 12
Achieved area per head 100.0 ft^2 (OK)
Max distance to walls 5.70 ft

Details, formula, and sources

The governing spacing is the smaller of the linear cap and sqrt(protection area per head), then heads per line, lines, the total head count, the achieved area per head, and the maximum wall distance (spacing / 2). For ordinary hazard the 130 ft^2 area cap forces a spacing near 11.4 ft, tighter than the 15 ft linear cap, so a 40 x 30 ft room takes 12 heads rather than a naive 15-ft-grid's 6. A rectangular-bay standard-spray estimate; obstructions, the beam rule, and minimum head spacing are separate checks. A takeoff aid, not a stamped sprinkler layout; a qualified fire-protection designer and the AHJ govern.

spacing = min(max_spacing, sqrt(area_per_head)); heads_per_line = ceil(length / spacing); lines = ceil(width / spacing); total = heads_per_line x lines; achieved = room_area / total; wall_max = spacing / 2.

NFPA 13 (Standard for the Installation of Sprinkler Systems), 2022, by name; the protection-area and linear-spacing caps by hazard class for standard-spray upright / pendent heads.

NFPA 13 is viewable free of charge through NFPA's online free-access reader; the min / sqrt / ceil layout arithmetic is public.

Estimate. AHJ and licensed professional govern.

Field names used by the API: room_length, room_width, area_per_head, max_spacing, spacing, heads_per_line, num_lines, total_heads, achieved_area_per_head, max_wall_distance

Hazard-class caps Light 225 ft^2 / 15 ft, Ordinary 130 ft^2 / 15 ft, Extra 100 ft^2 / 12 ft (hydraulically calculated), editable; whichever of the area or linear cap binds first governs the spacingNFPA 13 (2022)
Rectangular bay a flat-ceiling rectangular-bay estimate for standard-spray heads; obstructions, the beam rule, sloped ceilings, small rooms, and EC / ESFR heads have their own rulesNFPA 13 (2022)
Minimum spacing separate the minimum distance between heads (typically 6 ft, preventing cold-soldering) is a separate check this tile does not performNFPA 13 (2022)