Exhaust Fan Size for a Standard Bathroom
Part of our Ventilation & Hot Water guides.
Short answer: 80-110 CFM. Most hall and master baths fall here. Use 1 CFM per square foot: a 8x10-foot bathroom needs about 80 CFM, a 10x11 about 110 CFM.
Duct length matters
Fan ratings assume short, straight ducts. Each elbow and every extra few feet of flex duct cuts airflow. If your duct is long or has several bends, size up.
Placement
Install the fan near the shower (but not directly over it unless the fan is rated for that), and away from the door so air sweeps across the room.
Automation
A humidity-sensing fan runs until the room is dry, which is the most reliable way to stop mold. See the full CFM guide.
Example sizing
| Room | Area | Fan |
|---|---|---|
| 5x8 hall bath | 40 sq ft | 50-80 CFM |
| 7x10 hall bath | 70 sq ft | 80 CFM |
| 8x10 bath | 80 sq ft | 80-110 CFM |
| 10x10 primary bath | 100 sq ft | 110 CFM |
Fan + light combos
Many standard bathrooms have a single ceiling fixture. A fan with a built-in LED light replaces both. VEVOR's 110 CFM fans include LED options, and one model adds a humidity sensor and timer.
Switch options
- Timer switch: run for a set time after showering.
- Humidity-sensing fan: turns on and off automatically.
- Separate switches for fan and light, so the fan can run after you leave.
Frequently asked questions
Can a bathroom fan be too powerful?
Very large fans can be noisy and pull conditioned air out of the home; match size to the room.
Do I need a fan if I have a window?
Most codes accept an openable window, but a fan works in winter and when the window stays shut.
Can I use a 110 CFM fan in an 80 sq ft bathroom?
Yes; slightly larger fans compensate for duct losses.
Does a fan need a dedicated circuit?
Fan-only units usually don't; fans with heaters often do.
Should the fan be on the same switch as the light?
Separate switches or a timer let the fan run after you leave.
How do I know if my fan is working well?
Use the tissue test and check that mirrors clear within minutes after showering.