The differences between actual cubic feet per minute (ACFM), inlet cubic feet per minute (ICFM), free-air delivery (FAD) and Compressed Air & Gas Institute standard cubic feet per minute (CAGI-SCFM) were presented to improve compressed-air system design and equipment selection. The importance of mass flows (pounds of dry air per hour) which do not change when pressure, temperature, humidity or air density change was also discussed. Compressor type, inlet air density and installation are very important in energy-efficient compressed air design.