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Calculate the exact CADR (Clean Air Delivery Rate) rating you need for your room. This calculator determines minimum air purifier specifications based on your room dimensions and desired air changes per hour, providing CADR ratings for smoke, dust, and pollen.
CADR measures how much clean air an air purifier delivers per minute, measured in cubic feet per minute (CFM). The AHAM (Association of Home Appliance Manufacturers) tests air purifiers for three particle sizes: smoke (0.09-1.0 microns), dust (0.5-3.0 microns), and pollen (5.0-11.0 microns). A higher CADR means the purifier cleans air faster.
CADR ratings are tested independently and certified by AHAM. Not all manufacturers participate in AHAM testing, but those that do display the AHAM Verifide seal. When comparing air purifiers, CADR is the single most important performance metric - more important than marketing claims about "covers X square feet."
ACH describes how many times per hour an air purifier completely filters all the air in a room. For general home use, 4-5 ACH is recommended. For allergy or asthma management, target 5-6 ACH. For medical-grade filtration or immune-compromised individuals, hospitals use 6-12 ACH.
The relationship between ACH and CADR is direct: ACH = (CADR × 60) ÷ room volume in cubic feet. To achieve 4 ACH in a 12×15 room with 8-foot ceilings (1,440 cubic feet), you need a CADR of at least 96. However, CADR ratings differ by particle type, so we calculate separate requirements for smoke, dust, and pollen.
This calculator uses the industry-standard formula: CADR = (Room Volume × ACH) ÷ 60. We calculate three CADR ratings because air purifiers perform differently against different particle sizes:
When shopping for an air purifier, match the CADR rating to your primary concern. If you're worried about wildfire smoke, prioritize smoke CADR. For seasonal allergies, pollen CADR matters most. For general air quality, aim for a unit that meets or exceeds all three CADR minimums calculated above.
Most air purifier marketing materials list coverage in square feet, but this is misleading without knowing ceiling height. A 300 sq ft room with 8-foot ceilings (2,400 cubic feet) needs less CADR than a 300 sq ft room with 12-foot ceilings (3,600 cubic feet). Our calculator uses cubic feet to give you accurate CADR requirements.