Calculating duct dimensions is a cinch with the Ductulator! The Ductulator - Duct Sizing Calculator is a 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. One side uses English units, the other side uses Metric units. Includes a protective sleeve with ASHRAE recommended design air velocities for system components/applications.