Air Purifier Size Calculator
Enter your room size to get the exact CADR you need — and the right-size HEPA purifier to match.
Your Room
Length × width of the room. Not sure? A typical US bedroom is ~130–200 sq ft, a living room ~300–400 sq ft.
Standard is 8 ft. Higher ceilings mean more air volume to clean.
What size air purifier do I need?
The right size air purifier is decided by CADR (Clean Air Delivery Rate), not by the "up to X sq ft" number on the box. CADR — measured in cubic feet per minute (CFM) and verified by AHAM — tells you how much filtered air a unit actually delivers. To clean a room well you want enough CADR to cycle all the air in the room several times an hour (air changes per hour, or ACH).
- General cleaning: ~4 air changes/hr is a sensible baseline.
- Allergies & asthma: aim for ~5 air changes/hr so pollen and dust are cleared quickly.
- Pets: ~5 air changes/hr, and choose a unit with an activated-carbon layer for odor.
- Wildfire smoke: 6–7 air changes/hr to keep a clean-air room during smoke events.
Multiply your room's square footage by the ceiling height to get its volume, then use the formula above. Higher ceilings and higher air-change targets both push the CADR you need upward. When a single unit can't deliver enough clean air for a large or open-plan space, two smaller purifiers running together will out-clean one oversized claim — and let you cover more than one zone.