Cleanroom engineering tool
Air velocity & airflow calculator
Estimate the airflow through a unidirectional airflow zone from its effective cross-sectional area and average air velocity. See results in m³/h and CFM.
Calculate airflow
Results update as you type.
The open area of the plane perpendicular to the airflow.
The average velocity through the same cross-sectional plane.
For vertical flow, this is usually a horizontal plane; for horizontal flow, a vertical plane. Use area and velocity from the same plane.
How the calculation works
Volume flow rate equals the cross-sectional area multiplied by the average velocity normal to that area. The calculator converts the inputs to m² and m/s, then converts cubic metres per second into cubic metres per hour and CFM.
For example, an effective area of 2 m² with an average velocity of 0.4 m/s gives 0.8 m³/s, or 2,880 m³/h (about 1,695 CFM). The example velocity is for illustrating the arithmetic; select the velocity for the actual project.
Using the result in a cleanroom design
This calculation assumes a uniform average velocity across the entered effective area. Obstructions, nonuniform flow, leakage, and the location of the measurement plane can change the actual delivered airflow.
- For a vertical unidirectional zone, use a horizontal plane perpendicular to the downward airflow; for horizontal flow, use a vertical plane.
- Use the effective open area at the chosen plane and an average velocity measured or specified for that same plane.
- Confirm the airflow pattern and velocity with project-specific design and commissioning tests. This result alone does not establish an ISO cleanliness class.
Source notes: ASHRAE Handbook, Clean Spaces describes airflow, velocity, and unidirectional cleanroom arrangements. ISO 14644-3:2019 covers cleanroom performance test methods.