Duct Size Calculator
Enter airflow (m³/h), target air velocity and duct width to compute the required duct cross-section and height. For HVAC sizing and ventilation design.
Input Data
Results
At a glance:Duct sizing matches the cross-section to the airflow at a chosen velocity: area = airflow(m³/h) ÷ 3600 ÷ velocity(m/s), then for a rectangular duct height = area × 1000 ÷ width(mm). Keeping velocity in a sensible band (≈2.5–5 m/s supply) controls noise and pressure drop; too high wastes fan power, too low risks dust settling. Duct sizing follows continuity (Q = A·v) and is the first step in HVAC layout.
Formula
Area A = airflow(m³/h) ÷ 3600 ÷ velocity(m/s) (m²).
Height = A × 1000 ÷ width(mm).
Velocity check: keep within the design band (≈2.5–5 m/s supply).
$$A = \frac{Q}{3600\,v}$$$$h = \frac{A \times 1000}{w}$$How to Use
- Enter airflow (m³/h).
- Enter target air velocity (m/s).
- Enter duct width (mm).
- The tool returns area, height and a velocity note.
Case Studies
Office supply duct
Airflow 2000 m³/h, velocity 3 m/s, width 400 mm.
Area = 2000 ÷ 3600 ÷ 3 ≈ 0.185 m²; height = 0.185 × 1000 ÷ 400 ≈ 463 mm.
A ~400×460 mm rectangular duct keeps velocity near 3 m/s — quiet and efficient.
FAQ
What velocity should I use?
Supply ducts ~2.5–5 m/s, exhaust lower (1.5–3) to reduce noise; high-velocity saves space but raises fan power and sound.
Why size by area, not just width?
Both dimensions set the area that sets the velocity for a given airflow; fixing width alone leaves height undefined.
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References
Content review: Calculatorism Editorial Team. Results are for reference only; please refer to the relevant authorities for the official figures.