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CFM Calculator

Enter the room size and the air changes per hour to get the airflow needed in CFM and cubic metres per hour.

CFM calculator

Room volume: —
Required airflow: —
Airflow in cubic metres per hour: —
—
Airflow uses the standard relationship CFM = volume in cubic feet times air changes per hour divided by 60.

How to use the CFM Calculator

  1. Choose feet or metres and enter the room length, width and height.
  2. Set the air changes per hour you need for the room type.
  3. Read the required airflow in CFM and cubic metres per hour.

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Frequently Asked Questions

Common questions about the free online cfm calculator.

Multiply the room volume in cubic feet by the air changes per hour and divide by 60 to get cubic feet per minute.
CFM equals volume in cubic feet times air changes per hour, divided by sixty, because there are sixty minutes in one hour.
It is the number of times the whole volume of air in a room is replaced in one hour, and typical values run from 3 to 15.
Multiply cubic feet per minute by 1.699. For example 200 CFM is about 340 cubic metres per hour.
Kitchens are usually the highest at about 15 air changes per hour when cooking, while bedrooms need around 5 air changes per hour.
Yes. Enter the room size and the recommended air changes, and the result is the fan duty you need in cubic feet per minute.
Yes. The airflow depends on the whole room volume, so a taller room needs more CFM to reach the same air change rate.
No. The airflow figures are calculated in your browser, so the dimensions you enter are never sent anywhere.
Yes. It is free to use with no account, and you can size as many rooms and fans as you need.

Last updated: October 10, 2026