What is CADR?
Clean Air Delivery Rate (CADR) measures the volume of filtered air a purifier delivers per unit time, in cubic meters per hour (m³/h) or cubic feet per minute (cfm). It's tested separately for three particle types: smoke (0.09–1.0 µm), dust (0.5–3.0 µm), and pollen (5.0–11.0 µm).
How CADR is measured
Testing follows the ANSI/AHAM AC-1 standard. A purifier runs in a sealed 28.5 m³ chamber pre-loaded with a specific pollutant. Particle concentration is measured over time and compared against natural decay. The difference gives the CADR score.
CADR and room size: the 2/3 rule
AHAM recommends that a purifier's CADR (in cfm) should be at least 2/3 of the room area (in sq ft). In metric terms: multiply your room area in m² by 6.7 to get the minimum CADR in m³/h for approximately 5 air changes per hour.
Why three separate ratings matter
A purifier might have excellent dust CADR but weak smoke CADR if its carbon layer is thin. Missing CADR values (common with some brands) make meaningful comparison difficult. When a manufacturer publishes only one CADR category, treat the others as unverified.
Real-world vs. lab performance
Lab CADR is measured at maximum fan speed in a small sealed room. Real-world performance is lower due to: room leakage, furniture obstructing airflow, and typical use at lower fan speeds. Expect 60–80% of rated CADR during normal use.
