Smoke and Carbon Monoxide Detector Placement Calculator
Determine the minimum recommended number of smoke detectors and carbon monoxide (CO) detectors for your home based on NFPA 72 and UL standards. Enter your home's details below.
Fill in the details above and click Calculate.
Formulas Used
Smoke Detectors (NFPA 72 §29.8):
S = Floors + Bedrooms (1 inside each bedroom) + Bedrooms (1 outside each sleeping area / hallway) + Basement (1 if basement present) + Extra Rooms (1 per additional common room)
CO Detectors (NFPA 720 / UL 2034) — required when gas appliances or attached garage present:
CO = Floors (1 per floor) + Bedrooms (1 outside each sleeping area) + Basement (1 near furnace/water heater if basement present) + Garage (1 near garage entry if attached garage present)
Combination Unit Optimization:
Combo Units = min(S, CO) Standalone Smoke = S − Combo Units Standalone CO = CO − Combo Units Total Units = Combo Units + Standalone Smoke + Standalone CO
Assumptions & References
- NFPA 72 (National Fire Alarm and Signaling Code) §29.8: Requires smoke alarms on every level of the home, inside each bedroom, and outside each sleeping area.
- NFPA 720 and UL 2034: CO alarms required on every floor and outside each sleeping area when fuel-burning appliances or attached garages are present.
- U.S. Fire Administration (USFA): Recommends testing detectors monthly and replacing every 10 years (smoke) or 5–7 years (CO).
- One smoke detector per additional common room is a conservative recommendation; local codes may vary.
- "Outside sleeping area" means in the hallway immediately adjacent to bedrooms, not inside them.
- Combination (smoke + CO) units are counted once per shared location to minimize total units purchased.
- This calculator provides minimum recommendations. Local building codes may require more detectors.
- Interconnected detectors (wired or wireless) are strongly recommended so all alarms sound simultaneously.