Smooth-ceiling geometry
The layout keeps detector-to-detector spacing within the applicable spacing and checks every grid-cell corner against the maximum radius.
R = 0.7 × S
NFPA 72 planning assistant
Smoke Detector Spacing
Enter the room, ceiling, detector, and adopted-edition information. The calculator identifies the rule path, computes a conservative rectangular layout, and shows every suggested detector coordinate.
Required inputs
Smoke detector layout
NFPA 72 directs line-type integration detectors to the manufacturer's published instructions. A prescriptive grid is not calculated.
Use the maximum bounding length and width. The diagram is a preliminary coverage grid; verify every remote corner and obstruction on the actual plan.
Prescriptive layout available
6 detectors
Maximum spacing X—
Maximum spacing Y—
Wall offset—
Coverage radius—
Suggested plan layout
Diagram is proportional; dimensions govern.
Rule path
Detector coordinates
Coordinates are measured from the lower-left corner of the entered rectangle.
How the calculator works
Transparent equations and safeguards
Edition control
The chosen edition is carried into the rule path and printout. The 2025 smoke rules stop prescriptive calculation above a 40 ft ceiling.
Edition + device + ceiling → rule set
Important: This is a preliminary planning and field-verification aid, not a substitute for the adopted code, detector listing, manufacturer's instructions, engineered drawings, site conditions, or AHJ approval. Airflow, stratification, obstructions, ceiling pockets, environmental conditions, and local amendments can change the required design.