Duct Air Velocity Calculator
Calculate average air velocity in a rectangular duct from airflow and inside dimensions, with comparison to an editable target velocity.
Default project preview
720 ft/min
Duct cross-section
1.25 ft²
Target area requirement
1.286 ft²
Area difference
-0.036 ft²
Equivalent round diameter
15.1 in
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Duct area = inside width × inside height. Average velocity = airflow ÷ cross-sectional area. Required area at the target velocity = airflow ÷ target velocity.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Duct Air Velocity Calculator questions
Why use inside duct dimensions?+
Air flows through the clear internal cross-section, which may be smaller than the outside dimensions because of insulation or lining.
Does lower velocity always mean better performance?+
No. Lower velocity can reduce noise and friction but requires larger ducts and must still provide adequate air distribution.
Is equivalent round diameter a full conversion?+
It only matches cross-sectional area. Equal-friction conversion for rectangular ducts uses a different relationship.