Air Changes per Hour and Clearance Time
Air changes per hour from airflow and room size, with CDC's times to remove 99% and 99.9% of an airborne contaminant.
Open the tool → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Airflow unit
- CFM (cubic feet per minute)
- Supply or exhaust airflow
- 240
- Room unit
- Feet (volume in cubic feet)
- Room length
- 12
- Room width
- 10
- Room height
- 10
Result: 12 air changes per hour: about 23.0 minutes to remove 99% and 34.5 minutes to remove 99.9%.
The tool opens with these values already filled in. Replace them with your own.
What you enter
- Airflow unit: cubic feet per minute (cfm) or cubic meters per hour (m3h)
- Supply or exhaust airflow
- Room unit: feet and cubic feet (ft) or meters and cubic meters (m)
- Room volume (or enter the three dimensions)
- Room length
- Room width
- Room height
- Required air changes per hour, from your own standard (optional)
How this is calculated
Citation
CDC, Guidelines for Environmental Infection Control in Health-Care Facilities (2003), Appendix B, Table B.1 and its formula (page dated January 11, 2024); FDA, Sterile Drug Products Produced by Aseptic Processing (September 2004), for the 20 air changes reference. Read the sources: CDC Appendix B ↗, FDA 2004 guidance ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.