Air Changes per Hour Calculator
ACH = volume flow per hour ÷ room volume
Calculate an ideal air-change rate from volume flow and room volume.
Formula
ACH = volume flow per hour ÷ room volume
Worked example
Volume flow: 300 m³/h
Room volume: 100 m³
With these inputs, the result is 3 per hour.
How to use this calculator
- Identify the quantity you want to calculate.
- Enter your measurements in the units shown on each field.
- Read the result, which updates as you change the inputs.
- Check the assumptions below before applying the result.
Assumptions and limits
Does not establish ventilation adequacy, filtration efficiency, or contaminant removal in an actual room.
Precision and checking
Results are rounded for display. Use the most accurate measurements available, and avoid rounding your inputs unnecessarily. Extra decimal places in a result do not make an estimate more reliable.
To check a result, substitute the same input values into the formula shown above. Change one value at a time to understand how the quantity responds.
Frequently asked questions
What assumptions does this calculation use?
Does not establish ventilation adequacy, filtration efficiency, or contaminant removal in an actual room.
Are my inputs sent to a server?
No. The calculation runs locally in your browser. The result updates as you edit the inputs.
Sources & references
- NIST Guide to the SI — National Institute of Standards and Technology
