Are you thinking about renovating your bathroom? Are looking for the correct bathroom vent fan size for your bathroom? Bathrooms are not always airy in all houses, so exhaust or vent fans are required for ventilation.

There is a well-known quote;” When your home breathes, you breathe easier too.” This is the same with the bathroom’s ventilation. Vent fans exhale bad odor from the bathroom and help you feel refreshed in the bathroom.


If you want to know how to choose a right-sized vent fan for your bathroom, this article is what you need.


Note: To choose the right size for the bathroom vent fan, start with calculating how big your bathroom is. Consider the thumb rule or the multiplication rule to measure the capacity of the bathroom. For an average-sized bathroom, a 50 CFM vent fan is suitable. For more fixtures, calculate the area and consider 100 CFM vent fans to install.


Source; The Spruce


What Is A Standard Size For Bathroom Vent Fan?

Bath fan size

Credit: Lowes

There is no such standard size for vent fans. The size of the fan depends on the size of your bathroom. However, the duct has a standard size in all vent fans. If the fan is powerful enough for your bathroom, it would easily remove the moisture and odor from the area. But if not, it would be a flop for your bathroom. 


Vent fans are calculated by the ratings of cubic feet per minute. Well, as everyone asks for a standard size for vent fans, the Home Ventilating Institute recommends installing a fan with a rating of 1CFM per square foot. It would be counted as 50 CFM for an average-sized bathroom. 


While sizing the bathroom vent fan, one main thing to keep in notice is the duct. You have to consider the length and width of the duct. Any 4 inch ducts would work well with a 50 CFM vent fan. Other than that, the number of fittings of the duct and the elbows required are also elements to consider if you want a perfect sized vent fan.


Size Of Your Bathroom

Bath fan size completely depends on the size of your bathroom. Larger bathrooms would need bigger vent fans as compared to an average-sized bathroom. To calculate the size of your bathroom, multiply the length with the width of the room. This may give you an estimated area of your bathroom.


To find what size of vent fan would be perfect for your bathroom, you need to calculate the number of fixtures in the room. If your bathroom just has a shower and a toilet, 100 CFM vent fans would be accurate for it. But if it has a bathtub or a jetted tub along with the shower and toilet, you need to install a vent fan rated 200 CFM.


In bathrooms bigger than 100 square feet, the fan’s capacity needs to be increased with greater CFM. 


Consider The Capacity Of Bathroom

Before even thinking of installing any vent fan, consider the capacity of your bathroom. Ventilation problems usually occur because we try to fit more accessories into the room than its actual capacity. 


More stuff in one place suffocates the area and creates ventilation problems. A small 50 CFM vent fan can also work well if the bathroom is already airy. 

Methods Of Calculating CFM For Bathroom Vent Fan For Perfect Size

There are various typical methods to calculate the CFM for the perfect sized bathroom vent fans


Method 1: You can calculate the CFM by measuring your bathroom’s dimensions. It could be done by using a measuring tape to measure the walls’ length and the ceiling’s height. Through this method, you can calculate the volume of your bathroom, which would give you an estimated CFM for a perfect sized vent fan. 

“Kennedy Kitchens and Baths is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to”


Method 2: Another way to calculate the CFM is by calculating the area of your bathroom’s floor. This method is so simple. You just have to multiply the width and the length of the floor. This method also helps provide an estimated CFM for a suitable size of the vent fan. 

For example, the room has 100 square feet with a ceiling height of 12 foot.


100×12= 1200




Method 3: Use the thumb rule to calculate CFM for the vent fan’s perfect size. The rule of thumb asks you to choose 1 CFM for each square foot on the bathroom’s floor space. 


You can also add the additional CFM to the ceilings higher than 8 feet to get an estimated perfect size for a vent fan. 

If your bathroom is bigger than 100 sq feet, you need to include the fixtures and add the CFM required for each fixture. By doing so, you will be able to know whether to install a 50 CFM vent fan or a 100 CFM vent fan in the bathroom.

bath vent fan

Credit: Pinterest



Well, many people struggle to find the correct bath fan size for their bathroom. First of all, you need to start with knowing the standard size of any vent fan. Adding on, you must calculate the size of your bathroom by the cubic foot area. 

Moreover, you should be well aware of the capacity of your bathroom and should fit in enough stuff. These are enough for one to choose the right size for a vent fan in their bathroom. Best of luck!!



Jeff Kennedy

Editor in Chief

of Vade Mecum of Luxury Journal, multiple site contributor, writer, renovation professional He has been an active participant in the construction industry for 32 years, doing everything from design to finish work.
He shares his unique perspective on renovation and construction through writing about professional experiences. Jeff’s motto is that “enjoying what you do is the best feeling.” If you enjoy your job with friends, then you will never have to go to work!

Get featured in our magazine