How to Choose an Air Purifier for Your Room Size

CADR, room square footage and filter costs explained in plain English.

By the Give The Goods team · Oct 30, 2026

An air purifier that is too small for the room will run constantly and still struggle. Sizing it properly is mostly about one number.

CADR

Clean Air Delivery Rate measures how much filtered air a purifier delivers, in cubic feet per minute. A common rule of thumb is to choose a CADR of at least two-thirds of the room's area in square feet, so a 150 sq ft bedroom calls for a CADR of about 100 or more.

Check the stated room coverage carefully

Manufacturers quote coverage at different air-change rates. For allergies, look for a model rated for your room at four or more air changes per hour, or simply go one size up.

True HEPA and filter costs

True HEPA filters capture fine particles like dust, pollen and pet dander. Activated carbon helps with odors. Look up the replacement filter price before you buy; it is the real long-term cost.

Noise

If it is going in a bedroom, check the decibel rating on the lowest setting and whether there is a sleep mode that dims the lights.