About HVAC Duct Calculator

HVAC Duct Calculator is a professional-grade digital tool designed to help HVAC engineers, contractors, and home performance technicians calculate accurate ductwork sizing. Our mission is to provide an accessible, reliable, and free alternative to complex engineering software for day-to-day HVAC design and troubleshooting.

All calculations provided by this tool are based on established industry standards, primarily the equal friction method and ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) guidelines. We utilize the Darcy-Weisbach equation and standard air density assumptions to ensure engineering accuracy for both metal and flexible ductwork systems.

This tool was created to help professionals quickly verify branch and trunk sizes, estimate pressure losses, and ensure systems operate within recommended velocity limits. While our calculator is highly accurate for planning, it is designed to complement—not replace—a full Manual D duct design performed by a licensed professional.