How Many CFM for Bathroom Exhaust Fan (Calculator & Chart)

Bathroom fan CFM ranges from 50 CFM for a small bathroom to 200 CFM for a large bathroom.

Having the right size bathroom fan is essential for removing excess humidity that can allow mold to grow. It will also assist in removing common bathroom odors.

What’s here? This page includes a bathroom fan calculator to give you the best exhaust fan size for your purposes. You’ll also find a bathroom fan CFM chart for easy reference.

Terminology tip: Bathroom fans are also called exhaust fans, ventilation fans and extractor fans.

Bathroom Fan CFM Calculator

What size bathroom fan do I need? The answer is right here in this bathroom exhaust fan calculator.

Bathroom Fan CFM Calculator

To use the calculator, simply measure the square feet of your bathroom, usually done by multiplying length in feet times width in feet. Include shower stall and tub enclosure space.

Input the information and check off which fixtures you have, and Voila! You’ll have the right size bathroom fan for your room’s size and fixtures.

Why is the number of fixtures important?

Because each fixture represents the potential for more humidity released into the air.

What does CFM stand for? What is exhaust fan CFM? It is cubic feet per minute, and it refers to the amount of air that the fan moves every 60 seconds.

Bathroom Fan CFM Chart

The larger your bathroom, the more air the exhaust fan needs to move in order to keep the bathroom healthy – without excess humidity and with quick removal of odors.

This handy exhaust fan size chart gives you a good idea what size bathroom fan you need.

Bathroom SizeBathroom Size (square feet)Bathroom Fan CFM
5×735 sq ft50 CFM
5×840 sq ft50 CFM
8×864 sq ft70 CFM
8×1080 sq ft80 CFM
10×10100 sq ft100 CFM
12×12144 sq ft200 CFM
10×15150 sq ft200 CFM

Pro tip: Go up 1 size if the bathroom has a shower, bathtub or jetted tub, aka a Jacuzzi tub. Go up 2 sizes if it has multiple fixtures that might be in use at the same time or within a short period of time.

For example, a 70 CFM bathroom fan is large enough to handle a small or medium bathroom up to about 64 square feet – or 8’ x 8’.

However, if the bathroom also has a shower or tub/jetted tub, you should choose a larger fan – 80 CFM or 100 CFM.

An 80 CFM exhaust fan covers 80 square feet under typical conditions. If you have multiple high-volume fixtures like a shower or steam shower and a jetted tub, then an 80 CFM fan is only useful for about 64 square feet.

What Is The Highest CFM Bathroom Fan?

The highest CFM bathroom fans are 380 CFM. Those fans considered large bathroom exhaust fans start at around 240 CFM.

But choosing the largest CFM bathroom fan isn’t always the right choice. Consider the next section.

Can You Have Too Much CFM In The Bathroom?

Yes, your bathroom fan can be too large. The standard rule is at least 1 CFM per square foot.

Too many CFM in the bathroom have two negative consequences:

1). It will be loud. Bathrooms tend to have hard surfaces – tile floors and shower walls, glass shower doors, vinyl tub surrounds. And noise bounces around rather than being absorbed.

Consequently, when the bath fan CFM is too high, the noise might be uncomfortably loud.

2). You’ll waste energy. As a fan exhausts air, it creates negative pressure. As a result, it pulls air into your home from outside.

In winter, warm indoor air will be replaced with cold outside air.

In summer, you’ll send cooler indoor air outside, only to be replaced by warm, humid outside air.

Some exchange is inevitable. It’s how exhaust fans work. But too much CFM in the bathroom is detrimental.

Fan Size CFM for Small Bathrooms

50 to 70 CFM is the best size bathroom fan for rooms up to about 70 square feet. An 80 CFM fan or 100 CFM fan is a better choice if the room has a shower or jetted tub.

*Never go below 1 CFM per square foot of space. And definitely go larger if the room has multiple fixtures using hot water.

Exhaust Fan CFM for Regular Size Bathrooms

The right size bathroom fan for bathrooms of 70 to 100 square feet is 70 CFM to 150 CFM depending on the size and how many fixtures the bathroom has.

Bathroom Fan CFM for Large Bathrooms

100 to 200 CFM exhaust fans are the right size for bathrooms 10’x10’ and larger.

A general rule is 1 CFM per square foot plus adding 50-100 CFM per fixture.

So, a 10×10 bathroom fan size is 100 CFM with just a toilet. Add a shower or jetted tub, and the CFM should be 150 to 200.

Bathroom Fan for High Ceilings

It depends on the total cubic feet of the room: L x W x H = cubic feet.

A key aspect of bathroom fan sizing is that the fan should change the air every 8 minutes, or about 7-8 times per hour if it were to run non-stop.

Sizing the fan requires knowing the cubic feet of the room, which is length x width x height. Then, the right fan size is one that will move that much air in 7-8 minutes.

For example, an 8’ x 12’ bathroom with 9’ ceilings has 864 cubic feet of air. Divide that number by 8 (8 minutes), and you have 108.

Therefore, the fan should be roughly 100 to 120 CFM – that is, able to move 100 to 120 cubic feet per minute in order to move or exchange 864 cubic feet in 8 minutes.

Low Medium High Fan Settings

Brands like Broan, Nutone, Nautilus, FanTech, Delta and Panasonic make fans with multiple settings. This often requires a more complex – and costlier – switch, but you might find the performance options worth the extra cost.

Example: Let’s say you have a 10’ x 10’ bathroom, or 100 square feet. The minimum fan size is 100 CFM. But it might make sense to buy a larger fan like a 200 CFM fan.

Then, choose the fan speed based on the demand.

Toilet being used: 100 CFM setting.

Shower being used: 150 CFM setting.

Steam shower or jetted tub being used: 200 CFM setting.

Don’t forget to try the Bathroom Fan CFM Calculator above for precisely sizing a bathroom exhaust fan. 

Did you know? The US Department of Energy’s Energy Star program certifies bathroom ventilation fans. Find one for your home or ask a contractor about an energy efficient exhaust fan for your bathroom. 

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications. Protection Status