Air Purifier Size Calculator
The smoke CADR to look for, for one room.
Clean air
–
Estimate based on EPA and ENERGY STAR guidance (2/3 rule) and AHAM's wildfire advice. A purifier helps with particles; it is not a medical device.
Shop this size
We earn a commission if you buy through these links. Category pages and searches matched to your size, not ranked by commission.
How the CADR is worked out
CADR is in cubic feet per minute. The EPA and ENERGY STAR rule of thumb is a smoke CADR of at least two-thirds of the floor area for an 8 ft ceiling, which cleans the room's air about 5 times an hour. For wildfire smoke AHAM suggests about 1 cfm per square foot (7.5 air changes an hour at 8 ft). We scale both for your ceiling height: CADR = area × height × air changes ÷ 60.
What CADR do I need for my room?
The common rule is a smoke CADR of at least two-thirds of the room's area in square feet, for 8 ft ceilings. A 300 sq ft room needs at least 200 cfm. For wildfire smoke, aim higher: about one cfm of CADR per square foot.
What is CADR?
Clean Air Delivery Rate: how many cubic feet per minute of clean air a purifier delivers, tested for smoke, dust and pollen. Use the smoke figure; it is the hardest of the three and usually the lowest.
Sources: EPA guide to air cleaners in the home; ENERGY STAR air cleaner guidance; AHAM wildfire-season advice.