Duct Size Calculator
Estimate preliminary round and rectangular duct dimensions from airflow and target velocity, plus duct surface area and material cost.
Default project preview
14 in diameter
Required flow area
1 ft²
Rectangular duct
17 × 9 in
Raw round diameter
13.5 in
Duct surface area
130 ft²
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.
Flow area = volumetric airflow ÷ velocity. Round diameter = √(4 × area ÷ π). Rectangular width and height use the entered aspect ratio and round up.
BuildMeter Guides
Understand the measurements and assumptions
Use these visible reference guides before changing project inputs or planning allowances.
FAQ
Duct Size Calculator questions
Does this calculate duct pressure loss?+
No. Pressure loss depends on duct roughness, length, fittings, transitions, filters and airflow.
Why round duct dimensions up?+
Rounding up preserves at least the calculated flow area at the selected velocity.
Can high air velocity cause noise?+
Yes. Velocity, fittings, grilles and duct construction all affect noise and comfort.