Air Purifier Sizing Calculator
CADR ratings only mean something against your room volume. Enter your room size and how many times per hour you want the air cleaned, and get the CADR to shop for.
Your results
Worked example
A 20 m² bedroom with a 2.4 m ceiling, targeting 4 air changes per hour:
- Room volume: 20 × 2.4 = 48 m³
- Required CADR: 48 × 4 = 192 m³ per hour
- In the CFM units most packaging uses: 192 × 0.5887 = 113 CFM
Shop for a purifier with a CADR of at least 192 m³/h (113 CFM) on a speed you can tolerate listening to, not just on its loudest turbo setting.
How this calculator works
This is a sizing guideline only. CADR is measured on the highest fan speed, and real rooms have furniture, drafts, and doors opening, so sizing one step up and running a quieter speed usually cleans better in practice than an exact-size unit on turbo.
Common questions
Which CADR number should I compare, dust, pollen, or smoke?
Manufacturers list three CADR values. Smoke CADR is the lowest and the strictest, and it is the one that matters during Canadian wildfire smoke season. Compare smoke CADR against the requirement shown here to be safe.
Can one purifier cover my whole home?
Not effectively. Air does not circulate well between rooms with doors, so purifiers are sized per room, with priority on bedrooms where you spend a third of your day breathing.
Estimates only. This is a sizing guideline only, provided for planning purposes, and is not health or medical advice. People with respiratory conditions should follow their clinician's guidance on air cleaning. Mississippi Maple accepts no liability for purchase decisions made using this calculator.