Fan airflow calculator
Find the airflow a room needs for your target air changes per hour or turnover time, in m³/h, L/s and CFM, and how many fans of a given rating reach it.
Room sides up to 1,000 m, with the room volume (entered, or length × width × height) up to 1,000,000 m³; targets above 0 and up to 1,000 air changes per hour, or 0.06 to 100,000 minutes per change; fan rating up to 100 m³/s. Calculated on your device; download a JSON report and a CSV of results. This calculator uses the room and target fields only. Results update as you type. Up to 1,000,000 characters.
Your result
How to use Fan airflow calculator
- Enter the room length, width and ceiling height, or its known volume.
- Enter your target as air changes per hour or minutes per full air change.
- Optionally enter the rated airflow of one fan to get a fan count.
- Review the required airflow and download the report or CSV.
Useful next steps
Airflow from volume and air changes
Required airflow is room volume multiplied by air changes per hour, q = n V (Engineering ToolBox, Air Change Rates, checked 16 October 2026). A 4 × 3 × 2.5 m room holds 30 m³, so 6 air changes per hour needs 180 m³/h, which is 50 L/s or about 105.9 CFM.
Choose your own target
The target comes from you, for example from a product guide or local guidance. A turnover time is converted with 60 minutes divided by the minutes per air change. This calculator does not recommend a rate or check building or health codes.
Fan count
The fan count divides the required airflow by one fan’s rated airflow and rounds up. Ratings are usually measured with little resistance, so ducts, grilles and filters reduce real airflow. Complete mixing is assumed. Unit conversions use NIST SP 811 factors.