Air Purifiers · Tool
CADR calculator by room size
Most CADR numbers on a box mean nothing without your room's size. Enter your floor area, ceiling height, and how many air changes per hour you want, and this tool calculates the minimum CADR you need — and which purifier on our list meets it.
Floor area
120 sq ft
Room volume
960 ft³
Recommended CADR
80 CFM
Our 4 air purifiers against your target
For this room at 5 ACH, the Coway Airmega 400 is the cheapest option on our list that meets the target.
Formula: required CADR (CFM) = room volume (ft³) × target ACH ÷ 60. This is the standard ACH-based sizing formula, not a Picksights-specific calculation — see the sources section below for where each recommended ACH value comes from.
Sources
- CDC's minimum-5-ACH recommendation (May 12, 2023): archive.cdc.gov
- AHAM — air filtration standards and CADR certification: ahamverifide.org
- Each product's CADR: cited on its own product page (see main ranking).
Frequently asked questions
What is ACH, and why does the CDC recommend 5?
ACH (air changes per hour) measures how many times a room's full volume of air gets filtered in one hour. The CDC recommended a minimum of 5 ACH in May 2023 to reduce the risk of airborne particle transmission in occupied spaces; AHAM recommends the same figure for healthy indoor air, and ASHRAE recommends 6 ACH specifically for classrooms.
How is this different from the EPA's CADR ≥ two-thirds-of-floor-area rule?
Both are valid sizing methods at different levels of detail. The EPA's rule is a quick shortcut that only uses floor area. This calculator uses the room's actual volume (area × ceiling height) and an explicit ACH target, so it's more precise in rooms with unusually high or low ceilings — where the quick rule can under- or over-size the machine you need.
Which ACH target should I pick?
4 ACH is reasonable for general use in a room with no specific issues. 5 ACH is the CDC's and AHAM's recommended minimum for most homes. 6 ACH makes sense if you have allergies or pets in the house. 8 ACH is the figure to target during wildfire smoke events, when clearing speed matters more than it does in everyday use.
What if none of the purifiers on my list meet the target?
For very large rooms or high ACH targets, the real alternative is running two smaller units instead of one — the combined CADR of two machines can cover a volume that neither one covers alone.
Full ranking: Best Air Purifier →
Guide: Air Purifier Buying Guide →
Also see: Best for Large Rooms →
Also see: Best for Wildfire Smoke →
Also see: Best for Allergies & Pet Dander →