Air
Clean Air Delivery Rate
CADR
A rating for portable air cleaners, in cubic feet per minute, combining how much air a machine moves with how efficiently it removes particles. Reported separately for smoke, dust and pollen.
In more detail
CADR comes from ANSI/AHAM AC-1, which runs the machine in a sealed chamber of defined volume, injects a test aerosol, and measures how much faster the concentration falls with the unit running than it does on its own. The result is expressed as the volume of perfectly clean air per minute that would produce the same decay — a useful abstraction, because it collapses airflow and efficiency into one number that can be compared across machines.
Three figures are published because particle size changes the answer. Smoke represents the smallest range, roughly 0.09 to 1 micrometer, and is the number worth reading for combustion and wildfire particles. Dust covers roughly 0.5 to 3 micrometers, pollen 5 to 11. A machine can post a strong pollen figure and an unremarkable smoke figure.
Two limits matter more than the number itself. The rating is measured at the highest fan speed, which is frequently the speed nobody uses, so the clean air actually delivered in a bedroom is whatever the unit produces at a tolerable noise level. And CADR is a particle measurement only: it says nothing about gases, odors, or formaldehyde, regardless of what sorbent the machine contains.
Why it matters
It is the only figure that lets two portable air cleaners be compared on the same basis, which in a category full of unverifiable claims is worth a great deal. The common sizing heuristic is that smoke CADR should be at least two-thirds of the room's floor area in square feet, at an eight-foot ceiling. Treat that as a floor rather than a target: buying more capacity than the room needs is what makes it possible to run the machine on a low, quiet setting and still clear the air.
The common misunderstanding
That the rating describes the machine in your room. It describes the machine in a sealed chamber at full speed, with no doors, no furniture, no continuing particle source, and nobody trying to sleep. Every one of those differences reduces what arrives. The comparison between two units is reliable; the absolute number is a ceiling.
Related terms
On Compound
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Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.