CADR — Clean Air Delivery Rate — is the single most useful spec on a portable air purifier. Developed and verified by the Association of Home Appliance Manufacturers (AHAM) under the ANSI/AHAM AC-1 test method, it reports, in cubic feet per minute, how much genuinely clean air a unit puts out. Devices carry three separate scores — for tobacco smoke, dust, and pollen — because particle size changes the result.
CADR matters because it combines two things that marketing usually separates: how good the filter is and how much air the fan actually moves through it. A high-grade filter on a weak fan still delivers little clean air. A verified CADR is measured on the whole machine, so it can't be gamed by quoting filter efficiency alone.
To size a unit, use AHAM's 2/3 rule: the CADR should be at least two-thirds of the room's floor area in square feet. A 300-square-foot room wants a CADR of about 200 or higher. That target is set so the purifier achieves roughly four to five air changes per hour in a standard 8-foot-ceiling room — enough turnover to matter for allergens and smoke. When you're comparing portable cleaners or judging a whole-home recommendation, CADR is the apples-to-apples number; a product that won't publish one is asking you to take filtration on faith.