How to Size Ducts Using Velocity
When this applies
Use this guide for first-pass duct sizing when you want a fast area estimate before moving into detailed pressure-loss and noise calculations.
Tool to use
Cross-section from airflow and target velocity — round diameter or rectangular second side.
Open Duct Size & Velocity Calculator →Steps
- 1Set airflow and a target velocity appropriate for the duct type and project stage.
- 2Compute required cross-sectional area from continuity.
- 3Convert that area into a round diameter or one missing rectangular side.
- 4Review whether the result is still realistic for installation and acoustic expectations.
- 5Move to detailed loss and balancing methods when the layout becomes fixed.
Examples
- Comparing two candidate velocity limits for a main supply branch.
- Checking whether an available duct width forces an unreasonable height.
What to avoid
- Treating a velocity-only result as a final duct design.
- Ignoring acoustic and spatial constraints after the first sizing pass.
- Mixing airflow units without converting them consistently.
Related tools
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FAQ
Does this include pressure drop?
No. It only converts airflow and target velocity into area and size.
Can I use the same velocity target everywhere?
Not usually. Main trunks, branches, and terminals often have different practical velocity ranges.