Heating, Cooling & Ventilation calculator
CFM Calculator
Calculate required airflow in CFM and m³/h from room volume and target air changes per hour.
Calculate required airflow in CFM and m³/h from room volume and target air changes per hour. For a reliable estimate, measure the real project rather than relying on nominal room or product sizes. The input most worth checking is room volume and target ACH. Ventilation requirements depend on occupancy and room use as well as volume. Check the applicable design guidance before selecting fans or ducts.
What you need to enter
The CFM Calculator uses the following project information to calculate the result.
- Room volume
- Air changes per hour
Calculator result
Required airflow (CFM / m³/h)
How the CFM Calculator works
For required airflow in CFM and m³/h from room volume and target air changes, the calculator uses airflow = room volume × ACH ÷ time conversion. The mathematics is only one part of the estimate: getting room volume and target ACH right usually matters more to the real-world result than extra decimal places. Unit conversion happens before the calculation.
CFM Calculator worked example
CFM Calculator example: a 2,120 ft³ room with a target of 6 air changes per hour needs about 212 CFM because airflow = room volume × ACH ÷ 60. Fan selection must then account for duct resistance and delivered airflow. Use the numerical result as the starting point, then verify room volume and target ACH against the material, layout or equipment actually being used.
Important calculation assumptions
For required airflow in CFM and m³/h from room volume and target air changes, ventilation requirements depend on occupancy and room use as well as volume. Check the applicable design guidance before selecting fans or ducts.
Frequently asked questions
What project details should I have ready for the CFM Calculator?
For required airflow in CFM and m³/h from room volume and target air changes, use a measured or calculated room volume and the target air-change rate. Keep airflow units consistent when converting between CFM and m³/h. This keeps the calculation tied to the actual job rather than a generic assumption.
What can cause room volume and target ACH to differ from my first estimate in the CFM Calculator?
Do not chase extra decimal precision in the CFM Calculator until you have realistic values for room volume and target ACH. Ventilation requirements depend on occupancy and room use as well as volume. Check the applicable design guidance before selecting fans or ducts.
Can I select final equipment from the CFM Calculator result?
Use the airflow result as a ventilation target, then account for occupancy, duct resistance, fan performance and the ventilation guidance applicable to the room type. That is the practical way to carry the CFM Calculator result into the next step.