Air › Room size and CADR

Air cleaner size by room: CADR and air changes per hour

Enter your room and the smoke CADR printed on an air cleaner's label. You get the room area and volume, the air changes per hour that CADR gives in that room, and the CADR the published sizing rules name for a room of that size.

How it is worked out

• Air changes per hour (ACH) = CADR in cfm × 60 ÷ room volume in cubic feet. This is the formula CDC NIOSH uses in its ventilation FAQ.
• 2/3 rule (AHAM; EPA's sizing table uses the same ratio): a tobacco-smoke CADR of at least two thirds of the room area in square feet, for an 8-foot ceiling. Example from EPA's table: 300 sq ft → 195 cfm.
• Wildfire-smoke rule (AHAM): a smoke CADR equal to the room area in square feet.
• Higher ceilings: EPA and AHAM say to size up above 8 feet. We scale by ceiling height ÷ 8, as in CDC NIOSH's worked example (300 sq ft at 11 ft: 200 × 11/8 = 275 cfm).
• Unit conversions: 1 m = 3.28084 ft; 1 cfm = 1.699 m³/h.

CADR values for certified models are listed in AHAM's directory (linked below). We do not rank or recommend models.

Sources (checked 7 November 2026)

• US EPA, Guide to Air Cleaners in the Home (2nd edition; page updated 1 October 2026): sizing table and 8-foot ceiling note
• AHAM Verifide, Air Filtration Standards: the 2/3 rule and the wildfire-smoke rule
• AHAM Verifide, Directory of certified room air cleaners (CADR values per model)
• CDC NIOSH, Ventilation FAQs: ACH = airflow × 60 ÷ room volume, and the ceiling-height adjustment
• US EPA, DIY Air Cleaners: what the CADR measures
• US EPA, Research on DIY Air Cleaners to Reduce Wildfire Smoke Indoors: CADR test method in a room-sized chamber

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