Duct Equivalent Diameter Calculator

Rectangular Duct Equivalent Diameter

Calculate Rectangular Duct Equivalent Diameter

Kindly enter the preferred width and height of your duct to calculate the equivalent diameter:

Imperial (IP)
Duct Width
inch
Duct Height
inch
Metric (SI)
Duct Width
mm
Duct Height
mm

How to Calculate the Equivalent Diameter of a Rectangular Duct

Based on the duct design chapter of the ASHRAE Handbook of Fundamentals, the equivalent diameter of a rectangular duct is calculated using the below formula:

De = 1.3 (ab)0.625 / (a+b)0.25

where,
De = Circular equivalent of rectangular duct for equal length, fluid resistance and airflow (inch or mm)
a = Length one side of duct (inch or mm)
b = Length adjacent side of duct (inch or mm)

Convert Cubic Meter per Hour to Litre per Second

Enter your airflow in CMH (m³/hr) to convert into litre per second (L/s):

From
CMH (m³/hr)

Convert Feet per Minute to Meter per Second

Enter your velocity in FPM (ft/min) to convert into meter per second (m/s):

From
FPM (ft/min)