A CFM measuring device is a tool used to measure the amount of air that is being moved through a system. This is important to know in order to properly size a ventilation system, as the amount of air being moved can affect the efficiency of the system. CFM stands for cubic feet per minute, and is the standard unit of measure for air flow. A CFM measuring device is typically a handheld device that can be used to measure the amount of air being moved through a system. It works by measuring the pressure differential between two points, which can then be used to calculate the air flow rate. The device will also usually display the CFM rate, as well as other relevant information such as temperature and humidity. By using a CFM measuring device, one can ensure that their ventilation system is properly sized and running efficiently.