Air Purifier CADR Sizing
Minimum CADR for your room and use case.
Minimum CADR (cu ft/min)
120
Room: 180 sq ft · 1440 cu ft
Methods
Room volume × ACH ÷ 60120
AHAM 2/3 rule (sq ft × 0.66)119
Air changes per hour by use case
- Living room, light filtering: 2–3 ACH
- Bedroom, moderate: 3–5 ACH
- Allergies or pets: 5–6 ACH
- Wildfire smoke or asthma: 6+ ACH
CADR (Clean Air Delivery Rate) is the volume of filtered air a purifier produces per minute, certified by AHAM. The 2/3 rule (sq ft × 0.66) is AHAM's recommendation for normal indoor air. For wildfire smoke or allergies, double it. Look for CADR for smoke and pollen on the box; dust CADR is least useful.
About
Enter room dimensions and target air changes per hour. Get the minimum CADR (Clean Air Delivery Rate) needed. Includes the AHAM 2/3 rule for general use and a stricter formula for wildfire smoke or allergies.
How to use
- Enter room size and ceiling.
- Pick target air changes/hour.
- Read minimum CADR.
FAQ
What ACH for wildfire smoke?+
6 or higher. Most apartment-class purifiers can hit 4–5 ACH for a bedroom; for an open living room you usually need a second unit or a bigger one.