Definition: Cubic Feet Per Minute (CFM) is a measurement for finding the air volume velocity and it is commonly used for measuring the air flow in heating or cooling diffuses. CFM is also used as a rating and it depends on your room size to ensure adequate ventilation. Formula: CFM = (fpm * area) Where, 'fpm' denotes feet per minute. 'ft' denotes area in square feet. Example : Given, Feet per Minute = 20 fpm, Area in square feet = 55 ft2. To Find, Cubic Feet Per Minute Solution : Substitute the value of FPM=20 and Area=55 ft2 in the formula, CFM= (fpm * area) = 20 * 55 = 1100.