Duct Sizing Calculator
Calculate the round duct diameter and rectangular equivalent for a given airflow and velocity.
How to Use the Duct Sizing Calculator
- Enter the design airflow in CFM.
- Enter the design velocity in FPM (default 700).
- Click Calculate for round diameter and rectangular equivalent.
Casos de Uso
- •Residential HVAC duct sizing.
- •Commercial air handling unit design.
- •Ventilation system design.
- •HVAC contractor estimating.
Fórmula
D = √(4 × Q / (π × v)) × 12 inches. Rectangular equivalent: W × H where W = 1.3D, H = W/2.
Preguntas Frecuentes
What velocity should I use for ducts?
Main ducts: 700–900 FPM. Branch ducts: 500–700 FPM. Return ducts: 400–600 FPM.
What is the rectangular equivalent?
The rectangular duct that has the same airflow capacity as the calculated round duct at the same velocity.
What is CFM?
Cubic Feet per Minute — the volume of air moved per minute through the duct.