HVAC Duct Sizing, Airflow CFM, Velocity & Equivalent Rectangular Duct Estimator
Calculate supply and return air duct dimensions: round duct diameter (inches & mm), rectangular duct cross-section (WxH), airflow volume (CFM & m³/h), and design air velocity (FPM).
Recommended Round Duct Diameter (Inches)
Calculator Inputs
Recommended Round Duct Diameter (Inches)
Round Duct Metric Diameter (mm)
Airflow Volume in Cubic Meters / Hour (m³/h)
Estimated Cooling Capacity Equivalent (Tons AC)
Equivalent Rectangular Duct Width (at 10" Height)
Required Net Duct Cross-Section Area
Airflow Volume: CFM vs. m³/h Breakdown
ASHRAE standard recommended residential velocity is 700-900 FPM in main trunks and 500-700 FPM in branch ducts to prevent air noise.
All engineering calculations, structural estimates, and electrical sizing metrics are provided for preliminary estimation only. Always ensure compliance with relevant statutory building codes and occupational safety standards, verified by a certified professional engineer before practical implementation.
Calculation Methodology
Duct Area (sq ft) = CFM / Velocity (FPM). Round Diameter (in) = sqrt((Area * 4) / π) * 12. Equivalent Rectangular Dimensions: Area = Width * Height.
Frequently Asked Questions
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