What is CADR in an air purifier?

What CADR means

CADR stands for clean air delivery rate: the volume of filtered air a purifier delivers in an hour.

The US Environmental Protection Agency advises choosing a portable air cleaner whose CADR is large enough for the room, and notes that the higher the CADR, the more particles it can filter and the larger the area it can serve (EPA, Guide to Air Cleaners in the Home).

The same guide notes that the CADR rating system is for particles only. It does not describe how well a purifier removes gases or odours.

m³/hr and CFM

CADR is given either in cubic metres per hour (m³/hr) or in cubic feet per minute (CFM), the unit common on products sold in the United States. One CFM is about 1.7 m³/hr.

The Air Purifier XR2 has a CADR of 255 m³/hr, which is about 150 CFM.

Using CADR for your room

Divide the CADR by the volume of the room. The result is how many times per hour the purifier can, on paper, pass all of the room's air through its filter. This is called air changes per hour.

Illustrative example: a 300 sq ft room with a 10 ft ceiling holds 3,000 cubic feet of air, about 85 m³. With the XR2: 255 ÷ 85 = 3 air changes per hour. In a smaller room the same CADR gives more air changes per hour.

Real results depend on how well the room is sealed and on the outdoor air. Our room-size guide shows how to measure your room.

What CADR does not tell you

• How well the purifier removes gases or odours.
• How much electricity it uses. See how much electricity an air purifier uses.
• How long the filter lasts. See how often to change a HEPA filter.
• What grade of filter it uses. See HEPA filter grades explained.