CADR

CADR, or Clean Air Delivery Rate, measures how many cubic feet of filtered air a purifier delivers per minute for a specific pollutant, typically dust, smoke and pollen. It's an independent, tested rating rather than a marketing claim, which makes it the most reliable number for comparing air purifiers from different brands.

The rating only means something in relation to room size. A purifier with a high CADR number is wasted in a small bedroom, running at low, quiet speeds most of the time, while the same unit in a room too large for it will run loud and constant just to keep up, so matching CADR to square footage matters more than chasing the biggest number available.

For small apartments specifically, that usually means a mid-range CADR unit sized to the actual room rather than the whole unit, since closed interior doors limit how much air one purifier can realistically move between rooms. Filter type matters alongside CADR too, since a true HEPA filter handles fine particles that a basic filter passes through.