Fire safety
Smoke & Heat Detector Coverage
BS 5839-1 gives each smoke detector about 100 m² of flat ceiling and each heat detector about 50 m² - divide and round up.
Calculator
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How it works
Enter the floor area and detector type. The tool divides by the nominal coverage (smoke 100 m2, heat 50 m2), rounds up, and reminds you of the siting rules: 500 mm from walls, beams over 10% of ceiling height act as walls.
Frequently asked questions
How many smoke detectors per square metre?
Under BS 5839-1 a point smoke detector on a flat ceiling covers roughly 100 m2 (every point within 7.5 m). A 240 m2 open floor therefore needs at least three.
When do I use heat instead of smoke detectors?
Kitchens, garages and dusty spaces where smoke detectors false-alarm. Heat detectors cover less (about 50 m2, 5.3 m radius), so layouts need more of them.