Input Parameters
About This Calculator
- Size mode: Given airflow, recommends duct dimensions (rectangular ratio ~2:1, or circular diameter)
- Velocity mode: Given airflow and duct dimensions, calculates actual velocity
- Flow mode: Given duct dimensions and design velocity, calculates total airflow
- Typical recommended velocity: 3–6 m/s for supply ducts, 2–4 m/s for return ducts
How this duct sizing calculator works
This calculator uses the airflow continuity relationship between flow rate, duct area, and velocity. It can recommend a duct size from airflow, calculate velocity from dimensions and airflow, or calculate airflow from dimensions and velocity.
Inputs explained
- Calculation mode determines which value is solved: size, velocity, or airflow.
- Duct type selects rectangular or circular area formulas.
- Airflow is entered in m³/h and converted internally to m³/s.
- Rectangular width and height or circular diameter define the cross-sectional area.
- The selected standard changes the default sizing velocity and velocity assessment thresholds.
FAQ
Why does the calculator warn about high velocity?
High air velocity can increase pressure drop and noise, so the result includes a design suggestion.
Can I use the recommended size directly?
Use it as a starting point. Final duct design should also check pressure drop, noise criteria, fittings, branches, and balancing.
Why are rectangular sizes rounded?
Recommended dimensions are rounded to practical 10 mm increments for preliminary sizing.