Air velocity, which represents the distance traveled per unit of time, is commonly expressed in Linear Feet per Minute (LFM). By multiplying this air velocity by the air flow rate across the cross-sectional area of a duct, you can determine the volume of air flowing through the duct per unit of time. Volume flow rate is typically measured in Cubic Feet per Minute (CFM). The concept of air velocity is applicable in fields such as air conditioning, heating, and ventilation.