Construction
Ventilation CFM Calculator
Estimate required ventilation airflow in cubic feet per minute from room size and air changes.
Formula
Room volume = area multiplied by ceiling height. Required CFM = volume multiplied by air changes per hour, divided by 60 minutes.
How it works
Multiply floor area by ceiling height for volume, then apply the air changes per hour you need and divide by sixty to get cubic feet per minute. Use the result as a rough guide when comparing fans or ventilation units, and check local ventilation guidance for the room type.
FAQs
What ACH should I choose?
Bedrooms and living rooms need fewer changes than kitchens, bathrooms and workshops. Check guidance for your room type.
Is this the fan size to buy?
It is a rough airflow target. Duct losses and fan ratings mean the installed system should be checked by a professional.
Can I use metric units here?
This calculator uses feet and CFM. For metric results, use the air-changes calculator with cubic metres per hour.
Rough estimate only — consult a licensed professional for structural work before building.