Free Exhaust Fan Sizing Calculator
Calculate the exhaust fan CFM rating needed for bathrooms, kitchens, or utility rooms based on room volume and required air changes.
ft
ft
ft
ACH
Fan Rating Needed
85 CFM
Room Volume640 cu ft
CFM per Sq Ft Rule80 CFM
Fan Rating Needed vs Room Length
Exhaust Fan Sizing
CFM = Room Volume x ACH / 60
The HVI (Home Ventilating Institute) recommends a simpler rule for bathrooms: 1 CFM per square foot for rooms up to 100 sq ft, and 50 CFM minimum. For larger bathrooms, add 50 CFM per fixture (toilet, shower, tub). Kitchens need 100-400 CFM depending on cooking.
Example Calculation
10 x 8 ft bathroom, 8 ft ceiling, 8 ACH.
- 01Volume = 10 x 8 x 8 = 640 cu ft
- 02CFM = 640 x 8 / 60 = 85 CFM
- 03Square foot rule = 80 CFM
- 04Use at least an 80-90 CFM fan.
Frequently Asked Questions
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