Air purifier air changes calculator
Calculate equivalent air changes per hour and minutes per air change from room dimensions and the purifier’s CADR.
Enter the CADR for the particle type and fan speed you intend to use, not the unfiltered fan airflow. A particle filter does not supply fresh air or remove CO₂. No target ACH is assumed.
Enter your measurements, then calculate.
Method and limitations
Rectangular room volume = length × width × height. ACH = CADR in m³/h ÷ volume in m³; minutes = 60 ÷ ACH. NIST: 1 ft = 0.3048 m exactly; 1 CFM = 60 × 0.3048³ = 1.69901079552 m³/h. Assumes continuous operation and well-mixed air. These are equivalent clean-air changes, not fresh-air ventilation or a guarantee of complete pollutant removal.
Sources
- Guide to Air Cleaners in the Home — US EPA — consulted 2026-11-08,
- Handbook 44 (2023), Appendix C — Units of measurement — NIST,