SPECIFICATION SHEET • SI METRIC
CAT: HVAC

Duct Diameter from Airflow & Velocity

Estimate circular duct diameter and cross-sectional area from airflow and a target air velocity.

💡 Engineering Knowledge PrimerDuct sizing balances fan energy, noise, space, and pressure loss. This calculator reports the equivalent circular diameter for a declared airflow and target velocity; fittings, rectangular transitions, acoustics, and code constraints require a separate design review.
OPERATING LIMITS — Equivalent circular duct calculation only; verify rectangular transitions, fittings, leakage, acoustics, fire/smoke requirements, and system pressure loss.
INPUT DESIGN PARAMETERS (SI)
m³/h
m/s
CALCULATED SPECIFICATION OUTPUT
Equivalent Circular Duct Diameter
664.9 mm
Required Duct Area0.347 m²
Design Velocity8 m/s

Related planning checklists

This calculator appears in the following engineering planning checklists:

1. Factory Air Exchange & Ventilation2. Duct Diameter from Airflow & Velocity3. Fan Power from Airflow & Static Pressure4. Airflow Sensible Cooling Load

Technical Methodology & Engineering Principles

GOVERNING EQUATION
Area A = Volumetric Flow Q / Velocity v Equivalent Diameter D = √(4A / π)
Assumptions & Scope

Steady full-flow circular duct; uniform velocity; no fitting, leakage, roughness, acoustic, or system-effect correction.

Operating Range & Boundary

Airflow and target velocity must be positive.