Bathroom exhaust fan is an essential part of every bathroom. Choosing the right fan for your bathroom **starts with size**, Namely, you want to find out what size bathroom fan you need.

The size of a bathroom exhaust fan is measured in the amount of airflow they can receive. This air flow is measured in CFM or cubic feet per minute. CFM is just a unit that measures the amount of air flow.

Now, as we see, when you’re sizing a bathroom fan, you’re really asking this specific question:

“How many CFM for a bathroom fan?”

Large bathrooms require more CFM fans, smaller bathrooms require less powerful fans.

*Example:* a **50 CFM Bathroom Fan** a. is sufficiently sized to install in **47 square foot bathroom**, A 150 CFM bathroom fan can handle a bathroom of 141 square feet. We estimated a range of 8 feet in both of these calculations.

How do you calculate the CFM required for a bathroom fan? The best part about sizing a bathroom fan is that it is quite simple. As for HVAC rules of thumb, you only need to follow 1 rule:

The bathroom fan should achieve approx. **8 ACH (air change per hour)** Worth the CFM.

We will fully explain what ACH really means. The important thing here is that this simple rule states that you need about 1 cfm per square foot of bathroom for proper ventilation (ceilings of 8 feet).

we’ll show you how **Calculate How Many CFM Bathroom Fans** You need.

To help everyone else out, we created a . also made ** ‘Bathroom Fan CFM Calculator’**, You simply input the size of your bathroom in square feet and ceiling height, and the calculator will dynamically determine how many CFM bathroom fans you need.

You can complete the bathroom fan CFM calculator next, with ** ‘Bathroom Fan CFM Chart’**, The chart includes the exhaust fan CFM calculated for all bathrooms (from the smallest 20 square foot bathroom to the largest 500 square foot bathroom).

However, first, let’s take a look at how we determine how many CFM bathroom exhaust fans you need in a step-by-step process:

### How to determine what size bathroom fan you need?

*pay attention:* Thus you can manually (by hand) calculate the required CFM for the bathroom. Of course, the easiest way is to use the Bathroom Exhaust Fan Size Calculator (in CFM) below, or consult the Bathroom Fan CFM chart at the bottom of the calculator.

To operate properly, any bathroom exhaust fan must have enough power to replace all the air in a bathroom. **8 times per hour**, That’s what 8 ACH means. For example, you may be changing the air every 7.5 minutes to reduce humidity levels while showering.

We’ll explain the calculation first, and summarize the calculation in a short step-by-step process at the end of this chapter:

#### Calculating Bathroom Fan CFM By Hand

Bathroom exhaust fans can generate airflow anywhere from 40 CFM to 350 CFM. This is the same air flow that should be enough to ventilate your bathroom 8 times per hour.

*Example for 100 cfm bathroom fan:* Such a fan produces 100 cubic feet of airflow (100 cfm) every minute. This means that in 1 hour, a 100 cfm bathroom fan will generate 6,000 cubic feet of airflow (100 cfm × 60 minutes = 6,000 cubic feet).

Now this 6,000 cubic feet of airflow has to replace the entire bathroom room 8 times. That means we need to figure out how much air is in your bathroom.

We can do this by calculating the amount of air in the bathroom. For this we need to know 2 factors, namely:

- Bathroom
**square footage**, A 10×6 bathroom is 60 square feet, an 8×8 bathroom is 64 square feet, a 10×10 bathroom is 100 square feet. You know how it works. - Bathroom
**ceiling height**, The standard bathroom ceiling height is 8 feet. All the calculations you’ll find in the bathroom fan CFM chart on the use of 8 feet. Of course, some bathrooms may have ceilings of 10 feet or even 12 feet. This means we have to take into account more wind.

Here’s how to calculate the amount of air in the bathroom:

**Air volume (in the bathroom) = square footage × ceiling height**

*Example:* How much air is in an 8×10 bathroom with 8 ft ceilings?

Volume of air (8×10 with a ceiling of 8 feet) = 80 square feet × 8 feet = **640 feet ^{3}**

In this example, we need a fan that can turn 640 cubic feet of air 8 times per hour. How many CFMs should such a bathroom fan generate?

In 1 hour, the total airflow is 640 ft. should be^{3} × 8 = 5,120 feet^{3}, But as we know, the airflow of a bathroom exhaust fan is not expressed in cubic feet per hour (CFH). They are expressed in CFM or cubic feet per minute.

To convert CFH to CFM, we need to convert that 5,120 ft. will have to split^{3} From 60 (because 1 hour = 60 minutes). Here’s how we can finally get the bathroom fan’s airflow (in CFM):

**bathroom fan airflow** (8×10 with a ceiling of 8 feet) = 5,120 feet^{3} 60 minutes = **85 cfm**

This means that an 8×10 bathroom with a ceiling of 8 feet would require an 85 CFM fan.

*pay attention:* You can see that this is an 80 square foot bathroom and requires an 85 CFM fan. That’s pretty close to 1 cfm per square foot, isn’t it? If you have a bathroom ceiling of 8 feet, you can use 1 CFM per square foot of thumb without much loss in accuracy. If the ceiling is higher (or lower), you cannot use this rule of thumb.

Let’s summarize all this calculation in a simple step-by-step way:

#### Brief Step-by-Step Summary of Bathroom CFM Calculations

**Measure the length, width and height of the ceiling.**Example: 8×10 bathroom with ceiling of 8 feet.**calculate air volume**By multiplying length × width × height in the bathroom. Example: 8 feet × 10 feet × 8 feet = 640 feet^{3},**8. The volume of the room. multiply by**(due to the 8 ACH rule of thumb). Example: 640 feet^{3}× 8 = 5,120 feet^{3},**To calculate bathroom fan CFM, multiply the result by 60. divide by**(due to 1h = 60 minutes). Example: 5,120 feet^{3}60 =**85 cfm.**

Hopefully, this will help you figure out how much CFM you need for your bathroom.

We understand that this whole process can be a bit complicated. That’s why we designed the Bathroom Exhaust Fan CFM Calculator that simplifies the process:

## Bathroom Fan CFM Calculator

Simply input the square footage of your bathroom and ceiling height, and the Bathroom Exhaust Fan Size Calculator will dynamically calculate the required CFM *(You can slide from left to right to get a feel for how the CFM changes depending on the size of the bathroom or the height of the ceiling)*,

Using this calculator, you can determine what size bathroom fan you need. To make things even easier, we’ve calculated fan CFM requirements for the smallest 20 square foot bathroom to the largest 500 square foot bathroom.

You can find all the calculations in this bathroom fan size chart:

### Bathroom Fan CFM Chart

Bathroom Size (Sq. Feet): |
Required CFM: |

20 square feet | 21 CFM |

30 square feet | 32 CFM |

40 square feet | 43 CFM |

50 square feet | 53 CFM |

60 square feet | 64 cfm |

70 square feet | 75 cfm |

80 square feet | 85 cfm |

90 square feet | 96 cfm |

100 square feet | 107 CFM |

120 square feet | 128 CFM |

140 square feet | 149 cfm |

150 square feet | 160 cfm |

160 square feet | 171 CFM |

180 square feet | 192 CFM |

200 square feet | 213 CFM |

220 square feet | 235 CFM |

240 square feet | 256 CFM |

250 square feet | 267 CFM |

260 square feet | 277 CFM |

280 square feet | 299 cfm |

300 square feet | 320 CFM |

400 square feet | 427 CFM |

500 square feet | 533 CFM |

We hope you have found all this helpful. You can also find Universal CFM Calculator here; This can be helpful in some cases.

If you have any questions about the calculations or want our help in determining the CFM, you can comment below and we will try to help you as much as possible.

Thanks.

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