CFM Airflow Calculator
Find the airflow a room needs in cubic feet per minute. Enter the room dimensions and the target air changes per hour to size a fan or ventilation system.
How to calculate required CFM
- Enter the room length, width and height in feet.
- Choose the target air changes per hour for the space.
- Read the room volume and the required CFM.
- Pick a fan or system rated at or above that CFM.
Examples
20 by 15 ft room, 8 ft ceiling
2,400 cu ft at 8 air changes per hour
320 CFM
12 by 12 ft room, 9 ft ceiling
1,296 cu ft at 6 air changes per hour
129.6 CFM
Frequently asked questions
What is CFM?
CFM stands for cubic feet per minute, the volume of air a fan or system moves each minute. It is the standard way ventilation and HVAC airflow is rated.
How is required CFM calculated?
Multiply the room volume in cubic feet by the air changes per hour, then divide by 60 minutes. The result is the airflow in CFM.
How many air changes per hour do I need?
It depends on the room. Bathrooms often use 6 to 8, kitchens 7 to 8 and bedrooms 5 to 6. These are guidelines, so check local code and your fan maker.
Does ceiling height matter?
Yes. Taller ceilings mean more air volume, so the same air change rate needs more CFM. That is why height is part of the calculation.
Is this the same as sizing a bathroom fan?
It is one common method. Many bathroom fans are sized at 8 air changes per hour, which this tool computes when you enter the room volume and ACH.
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