Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. 82 Math for HVACR 5.8 Velocity Measurement Air velocity, or speed, is a measurement of the distance the air moves in a specificfi length of time. Air volume is the amount of air being moved. In the HVACR field, air velocity and air volume are widely used, as air is one of the primary mediums of heat transfer. TSI Incorporated 5.8.1 US Customary In the US Customary system, air velocity is measured in feet per minute (fpm), and air volume is measured in cubic feet per minute (cfm). 5.8.2 SI The SI unit used for air velocity is meter per minute (m/min), and for air volume cubic meter per minute (m3/min).