Air Purifier CADR Target Calculator

Match an air purifier to your room by calculating the clean air delivery rate required to hit your target air changes per hour. Provide the room size and desired ACH to instantly see the minimum CADR in cubic feet per minute (and cubic meters per hour) along with the room volume used in the calculation.

Measure length × width of the treated space.
Typical targets range from 4 ACH for bedrooms to 8+ for allergy/asthma relief.
Defaults to 8 ft if left blank.
Defaults to 100%. Enter the CADR lab-tested efficiency for the contaminant of concern.

CADR ratings are laboratory measurements. Real-world performance varies with filter maintenance, airflow obstructions, and pollutant sources. Verify purifier specs and replace filters as recommended.

Examples

  • 280 sq ft room, 5 ACH, 8 ft ceiling, defaults for efficiency ⇒ Minimum CADR: 186.67 CFM (317.75 m³/h) • Room volume: 2,240.00 cubic ft • Assumed ceiling height: 8.00 ft • Target ACH: 5.00 • Efficiency factor applied: 100.00%.
  • 420 sq ft living room, 8 ACH, 9 ft ceiling, 85% efficiency ⇒ Minimum CADR: 595.29 CFM (1,011.08 m³/h) • Room volume: 3,780.00 cubic ft • Assumed ceiling height: 9.00 ft • Target ACH: 8.00 • Efficiency factor applied: 85.00%.

FAQ

How do I estimate CADR for multiple rooms?

Run the calculator for each room separately or add their volumes together if your purifier will serve combined spaces without doors.

Can I account for two purifiers in the same room?

Yes. Divide the required CADR by the number of units you plan to deploy and ensure each purifier can deliver that share.

What ACH should I target for allergies or asthma?

Most allergists recommend 5–8 ACH in bedrooms and living spaces. Increase the ACH input toward 8 or higher for severe allergies or wildfire smoke.

Does the calculator handle CADR ratings for smoke, dust, and pollen separately?

Use the lowest CADR rating published for your purifier to stay conservative, or rerun the calculation with each rating to see how particle-specific performance compares to the target.

Additional Information

  • CADR is stated in cubic feet per minute; many international specs use cubic meters per hour, so both are provided.
  • The calculation assumes even air mixing and no leakage from adjacent rooms. Add a safety margin when dealing with smoke or wildfire seasons.
  • Use the efficiency field to adjust for filters that are less than 100% effective at the particle size you care about.
  • Higher ceilings increase room volume and therefore the CADR required to sustain the same ACH.

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