A coverage claim is only meaningful when its air-change rate and ceiling height are known. Work backward from CADR to see the room area corresponding to your own target. A larger advertised coverage figure may simply assume fewer air changes.
How to use
- Find the purifier clean air delivery rate and select its stated unit.
- Enter the target ACH and the room ceiling height.
- Compare the calculated floor area with the connected space you intend to clean.
How the calculation works
Room volume (m³) = CADR (m³/h) ÷ ACH. Floor area (m²) = volume ÷ ceiling height (m).
Example
A purifier delivering 300 m³/h provides 5 equivalent air changes per hour in 60 m³. With a 2.5 m ceiling, that corresponds to 24 m², approximately 258 ft².
Factors affecting the result
- A higher ACH target reduces the supported room size.
- A tall ceiling reduces floor-area coverage for the same room volume.
- Separate rooms do not necessarily share filtered air effectively through a doorway.
Frequently asked questions
Why is this area smaller than the box says?
Check the ACH and ceiling height behind the advertised coverage. A one-ACH coverage figure is five times the area of a five-ACH figure at the same ceiling height.
Can I add two purifier CADRs?
For two units in the same reasonably mixed space, adding their clean-air delivery is a useful estimate. It is less reliable for separate rooms.
Sources & methodology
Calculation basis: Physics-based airflow calculation. Methodology
- Guide to Air Cleaners in the Home, second edition — U.S. Environmental Protection Agency
Last updated: September 15, 2026