CFM stands for “cubic feet per minute” and is a measure of air flow, often used to describe the capabilities of heating, ventilation and air conditioning systems.

It describes the rate at which a certain volume of air moves in a certain period of time. In the case of a blower or fan, it indicates how much air it can move per minute. So for example, a **1,000 cfm** fan can remove all of the air from a box that is 10ft x 10ft x 10ft in one minute.

The most common use for this formula is when installing a bathroom fan.

1. If a bathroom is **8′** x **8′** with **8′** ceiling, that equals **512 cubic feet**.

2. If there’s a need to turn the air over **5** times in an hour, a total of **2,560 cubic feet** of air will need to be moved.

3. Take **2,560 cubic feet** , divide it by one hour (60 min), equals 42.6 cfm

The conclusion is that a fan of at least **42.6cfm** will be needed to do the job.