Duct Sizing Calculator is hand held rotating calculator used for sizing supply and return duct systems using the equal friction design method. This accurate, easy-to-use duct size calculator includes scales for friction loss per unit length, air volume, air velocity, round duct diameter and rectangular duct diameters. With single setting, the answer to any duct sizing problem may be read directly from the face of the Ductulator. One side uses English units, the other side uses Metric units. Conversion of units, English-to-metric, or vice versa, is accomplished by setting up a problem on the scales of one unit system, reversing sides of the Ductulator, and reading the converted values from the scales of the other unit system.