What size air purifier do I need?

The EPA gives a table of the minimum CADR (clean air delivery rate, in cfm) for rooms from 100 to 600 square feet with 8 ft ceilings. Enter your room to scale it, or enter a purifier's CADR to see how many times per hour it cleans your room's air.

The EPA says the chart is for estimation purposes and is based on an 8-foot ceiling. For other ceiling heights the calculator scales that figure in proportion to the height, and the air changes per hour (ACH) are our own arithmetic: CADR in cfm × 60 ÷ room volume in cubic feet. One cfm is about 1.7 m³/h.

Source: EPA, Guide to Air Cleaners in the Home, checked November 10, 2026.

General information only. These tools give estimates from the figures shown and what you enter. They are not medical advice and do not replace the maker's manual. Nothing you type is stored or sent.