Duct Sizer

HVAC air duct sizing · equal friction & velocity methods

Inputs

Duct Material

Airflow (CFM)

Air Temperature (°F)

Sizing Method

Equal Friction Velocity

Friction Rate (in.w.c./100 ft)

Results

Round Duct

— in. dia.

Velocity

—

Friction

—

Adjust Size

in. dia.

Rectangular Duct — Equal Friction Equivalent

— × — in.

Velocity

—

Friction

—

Aspect Ratio

—

Adjust Size

W H in.

⚠ Aspect ratio exceeds 4:1 — not recommended (SMACNA).