Duct Calculator

Enter known values for Air Flow Rate (CFM) and Friction Loss per 100FT of Steel Duct (inches of water).
Read computed values for Duct Diameter (inches) and Velocity (FPM).

Flow Rate (CFM):

Friction Loss (in. of water):

Diameter (inches):

Velocity (FPM):

Enter known values for Air Flow Rate (CFM) and Duct Diameter (inches).
Read computed values for Friction Loss per 100FT of Steel Duct (inches of water) and Velocity.

Flow Rate (CFM):

Diameter (inches):

Friction Loss (in. of water):

Velocity (FPM):

Equivalent Diameter: Diameter of a round duct that equates to the same pressure loss as the corresponding rectangular duct.
Enter the Length (inches) and Width (inches) of the Rectangular Duct.
Read computed values for Equivalent Round Duct Diameter (inches).

Length (inches):

Width (inches):

Equiv. Diameter (inches):

Equivalent Diameter: Diameter of a round duct that equates to the same pressure loss as the corresponding flat oval duct.
Enter the Long Axis (inches) and Short Axis (inches) of the Flat Oval Duct.
Read computed values for Equivalent Round Duct Diameter (inches).
This tool can be used to work backwards to convert a Round Duct Diameter to an Equivalent Flat Oval Opening based on job parameters.

Long Axis (inches):

Short Axis (inches):

Equiv. Diameter (inches):