Fire safety
Detector Spacing Check
The rule is a radius, not a grid: every point on the ceiling must sit within 7.5 m of a smoke detector - which allows about 10.6 m between detectors on a square layout.
Calculator
Fill in the fields above to see results.
How it works
Enter your planned spacing and the detector type. The tool checks it against the maximum square-grid spacing implied by the BS 5839-1 point radii (10.6 m smoke, 7.5 m heat).
Frequently asked questions
How far apart can smoke detectors be?
On a flat ceiling, up to about 10.6 m apart on a square grid - that keeps every point within the required 7.5 m. Corridors and beams change the arithmetic.
Do beams affect detector spacing?
Yes - BS 5839-1 treats beams deeper than 10% of the ceiling height as walls, splitting the ceiling into separate bays that each need coverage.