Air Purifier Room Size Calculator

How It Works

CADR (Clean Air Delivery Rate) is the standard measure of air purifier performance, rated in cubic feet per minute of clean air delivered. A higher CADR means faster air cleaning. The rule of thumb is to choose a purifier with a CADR at least two-thirds of your room area in square feet — so a 300 square foot room needs at least 200 CADR. For allergy and asthma sufferers, aim for 4 to 6 air changes per hour. HEPA filters capture 99.97 percent of particles 0.3 microns and larger, including pollen, dust mites, pet dander, and mold spores. Activated carbon filters (often combined with HEPA) handle odors, VOCs, and smoke. Avoid ozone-generating purifiers, which can irritate lungs. Filter replacement is an ongoing cost — budget $40 to $80 per filter every 6 to 12 months.