Smoke Detector Calculator — How Many Smoke Alarms Do I Need?
Enter your floor count, bedrooms and hallways to get the number of smoke detectors your home needs under NFPA placement rules. No sign-up, no data stored.
Smoke detectors needed
How smoke detector count is determined
- Bedrooms = one detector inside every bedroom.
- Hallways = one outside each sleeping area (hallway outside bedrooms).
- Floors = one per level, including the basement and finished attic.
- Total = bedrooms + hallways + floors.
These are the NFPA 72 minimums. For a finished basement or a hallway serving multiple bedrooms, the counts above meet code - consider extra units in kitchens, garages and workshops for early warning (with the right alarm type).
Home type → smoke detector reference
NFPA 72 minimum placements.
| Home | Bedrooms | Floors | Hallways | Total |
|---|---|---|---|---|
| 1-bed apartment | 1 | 1 | 0-1 | 2-3 |
| 2-bed ranch | 2 | 1 | 1 | 4 |
| 3-bed two-story | 3 | 2 | 1 | 6 |
| 3-bed + basement | 3 | 3 | 1 | 7 |
| 4-bed + attic | 4 | 3 | 2 | 9 |
Last updated: October 2026 · Local codes may require more (e.g. CO detectors near bedrooms). Verify your jurisdiction before installation.
Smoke detector FAQ
NFPA 72 requires one in every bedroom, one outside each sleeping area, and at least one per floor including the basement. A typical 3-bedroom two-story house needs about 5-6 alarms.
On the ceiling, at least 4 in from any wall, or on a wall 4-12 in from the ceiling. Keep them 10 ft from cooking appliances to avoid nuisance alarms and 3 ft from bathroom doors to avoid steam trips.
Yes - at least one per level, including the basement and finished attic. Fires spread through floor assemblies, and an alarm in the basement can warn of problems below before they reach the living floors.
Yes - interconnected alarms all sound together, which is critical at night when a fire starts in one room and you are asleep in another. Hard-wired with battery backup or wireless-linked battery units both meet the requirement.
Replace the unit every 10 years - the sensor degrades even if the battery works. Test monthly, change the battery at least yearly, and never paint over a detector.
Related calculators & guides
How Many Smoke Detectors Do I Need?
NFPA placement rules, alarm types and installation tips.
Read the guide →