About this tool
Velocity in a rectangular or round duct, or the duct size needed for a target velocity.
V = Q/(3600·A) with Q in m³/h and A in m²; D_h = 4A/P; sizing returns D = √(4A/π).
Formula: V = Q/(3600·A) A_rect = a·b A_round = πD²/4
Example: Duct shape = Rectangular, Mode = Velocity from size, Airflow (m³/h) = 3,600, Width a (mm) = 500, Height b (mm) = 400 → Velocity (m/s) = 5, Duct area (m²) = 0.2.
Pure continuity. Friction loss, fittings, roughness and fan pressure are not included.
Quick steps
- Enter your values — every field shows its unit.
- Press Calculate (or Try an example to see how it works).
- Read the results and copy them if you need them elsewhere.
The calculation runs in your browser. Nothing you type is sent to 1CLIK.
FAQ
How does the HVAC Duct Airflow Calculator work?
V = Q/(3600·A) with Q in m³/h and A in m²; D_h = 4A/P; sizing returns D = √(4A/π).
What should I keep in mind?
Pure continuity. Friction loss, fittings, roughness and fan pressure are not included.
Is my data sent anywhere?
No. The numbers stay on your device; the page only shows the result.