Download the duct sizing chart to keep on hand for all of your common lookups and calculations involved in planning ductwork DuctulatorHand held rotating calculator used for sizing supply and return duct systems using the equal friction design method. FPMinWg/ft. Note: Duct Dimensions are always Inner Dimensions. PLENUM/DUCT FITTINGS. Includes scales for friction loss per unit length, air volume, air velocity, round duct diameter, and rectangular duct diameters Download free duct sizing chart pd