How to Use a Ductulator for Sizing Ventilation Ducts

Using a ductulator, you can estimate the proper size and dimensions of the duct, the volume of airflow, the equivalent round and rectangular duct sizes, and the air velocity inside the duct.

How to read a ductulator (key components):

Pressure drop (in inches of water gauge) → inner blue scale

Airflow volume (in cubic feet per minute, CFM) → outer blue and red scales

Air velocity inside the duct (in feet per minute, FPM) → inner red scale

Round duct diameter (in inches) → inner Window

Rectangular duct dimensions (in inches) → inner and outer purple scales

Example:

For a duct carrying 5,000 CFM of air with a pressure drop of 0.1 inches of water per 100 feet, using the ductulator gives the following results:

Air velocity: 1,410 FPM

Round duct diameter: 25 inches

Equivalent rectangular duct options: 19" × 29", 23" × 23", or 42" × 14"