Duct Size & Velocity Calculator

Continuity only: A = Q̇/v, round D = √(4A/π), rectangular height from A and a known width. Does not apply friction, aspect-ratio noise rules, or SMACNA construction details.

Free · No limits · Runs in your browser

How to use

  1. 1Enter volumetric flow (m³/s, L/s, CFM, or gpm if reusing hydronics units).
  2. 2Enter mean velocity target in m/s.
  3. 3Pick round (diameter) or rectangular (supply one side, get the other).

Frequently asked questions

Are losses included?
No. This is area from Q and v only.
Is the rectangle aspect ratio checked?
No. You must verify noise, installation, and code constraints separately.

Engineering: Discipline-based calculators for fluids, electrical, HVAC, structures, and more — browser-first, with clear assumptions.

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