You should know that both metrics are equally essential but describe different things. The CFM of a leaf blower (cubic feet per minute) measures the strength of the air volume that comes out in one minute. For example, a leaf blower with a CFM of 200 should push 200 cubic feet of debris in one minute. The MPH (miles per hour) measures the speed at which air comes out of the machine in one hour. The perfect leaf blower has both a good MPH and a good CFM. A leaf blower can have high MPH, but if the volume of air exiting the is low, it still does not pack enough of a punch.