Bathroom Exhaust Fan CFM Calculator
Part of our Ventilation & Hot Water guides.
Enter your bathroom size to get a recommended exhaust fan size.
How it works
For bathrooms up to 100 sq ft we use 1 CFM per sq ft (50 CFM minimum), scaled for ceilings above 8 ft. Larger bathrooms use about 50 CFM per fixture, plus 100 for a jetted tub. This is a rule of thumb; long ducts need more.
Worked examples
- 6x8 bathroom, 8 ft ceiling: 48 sq ft → 50 CFM minimum; an 80 CFM fan gives headroom.
- 8x10 bathroom, 9 ft ceiling: 80 sq ft × 9/8 = 90 CFM → 110 CFM fan.
- 12x12 bathroom with jetted tub: fixture method, about 200 CFM → two fans.
Duct adjustments
Fan ratings assume minimal duct resistance. Long runs, flexible duct and multiple elbows reduce airflow; if your duct is longer than about 20-25 feet or has several bends, choose the next size up.
Noise
Sones measure perceived loudness. Under 2 sones is considered quiet; VEVOR's ceiling fans are rated at 1.5 sones.
Next steps
Once you know the CFM, compare fans in our buying guide and check the housing size and duct diameter against your ceiling.
Frequently asked questions
Is this calculator exact?
It applies common rules of thumb; long or bent ducts need a bigger fan.
Does the calculator account for duct length?
No; it applies the room-size rule. If your duct is long or has several elbows, choose the next fan size up.
Why is the minimum 50 CFM?
Common guidance and codes set about 50 CFM as the minimum intermittent airflow for a bathroom.
Should a separate toilet room have its own fan?
Ideally yes. Enclosed toilet rooms in large bathrooms benefit from their own small fan.
Can I use a bigger fan than recommended?
Moderately bigger is fine and helps with long ducts. Very large fans are louder and can depressurize tight homes.