Airflow for air changes Calculator: measuring notes and method
Measure the enclosed room volume
For a room with a sloping ceiling or different height zones, calculate non-overlapping volumes and add them before applying the specified air-change rate.
CHECK A PRACTICAL EXAMPLE
Ceiling height affects the volume
Compare a 6 × 4 m room at two heights, using an illustrative target of six air changes per hour.
2.4 m height
- Airflow required
- 345.6 m³/h
- Room volume
- 57.6 m³
3 m height
- Airflow required
- 432 m³/h
- Room volume
- 72 m³
Floor area alone is insufficient. The air-change target must come from the applicable design; calculated volume flow does not select a fan or account for pressure losses.
Fixed comparison in metric units. Values are illustrative unless linked to a recorded project; changing the calculator above does not change this example.
Formula
Airflow (m³/h) = room length × width × height × air changes per hour. One CFM ≈ 1.699 m³/h.
Worked examples in metric and imperial units
Illustrative values match Reset example and stay fixed when you edit the calculator. Both columns describe the same calculation; converted inputs are rounded.
Metric worked example
- Length
- 6 m
- Width
- 4 m
- Room height
- 2.4 m
- Target air changes per hour
- 6 changes/h
Airflow required: 345.6 m³/h
Imperial worked example
- Length
- 19.685 ft
- Width
- 13.1234 ft
- Room height
- 7.874 ft
- Target air changes per hour
- 6 changes/h
Airflow required: 203.4125 CFM
Follow the calculation
Lengths in this working are in metres.
- Room volume = 6 × 4 × 2.4 = 57.6 m³.
- Airflow = 57.6 × 6 = 345.6 m³/h.
Reviewed 19 October 2026. How calculations are checked · Report a correction