Best Air Purifier Size for a Bedroom

Size a bedroom purifier by smoke CADR, not by the "room size" on the box. For a standard 8 ft ceiling, a common target is a smoke CADR of at least two-thirds of the room's floor area in square feet, which is roughly five air changes per hour.

• Air changes per hour (ACH) = CADR (CFM) x 60 / room volume (ft³).
• Room volume = floor area (ft²) x ceiling height (ft).
• For an 8 ft ceiling and a 5 ACH target, CADR ≈ floor area x 2/3.
• For allergy or open doors, target higher: CADR ≈ floor area or more.

• 100 ft² bedroom, 8 ft ceiling: 100 x 2/3 ≈ 67 CFM minimum; 100 CFM for faster cleaning.
• 200 ft² bedroom: at least ~130 CFM; ~200 CFM if you want a strong margin.
• Open-plan area of 600 ft²: treat it as one space and target ~400 CFM or more.

• Noise at the speed you will run overnight, not just the sleep rating.
• Filter type: true HEPA plus carbon if odor matters.
• Filter cost and availability over a year.
• Sensor and auto mode, if you want it to react on its own.

• Trusting the box's "recommended room size" instead of CADR.
• Sizing one unit for several closed bedrooms.
• Ignoring noise until the unit is too loud to sleep next to.
• Forgetting that a dirty filter lowers effective airflow over time.

U.S. EPA, Guide to Air Cleaners in the Home; AHRI Standard 680 (CADR definition); manufacturer CADR ratings. Verify current ratings before buying.