Air Duct Size Calculator

Air Duct Size Calculator is a focused HVAC tool for professionals who need fast duct sizing, airflow checks, and clear pressure-related calculations. It is built for practical work: direct input, clear results, and quick access to the engineering values behind each calculation.

Use it to size round and rectangular ducts from airflow with either a target velocity or a target friction rate. You can review exact results, compare practical rounded sizes, and work through realistic options without relying only on a traditional ductulator workflow. The app also lets you analyze an existing duct, solve section pressure-drop relationships, estimate run loss, and compare round and rectangular conversions in one place.

Key capabilities:

• Size round and rectangular ducts by velocity or friction
• Analyze an existing duct from airflow, velocity, or friction
• Solve pressure-drop relationships for total pressure drop, friction rate, straight length, or added equivalent length
• Estimate run loss using straight length, equivalent length, fitting loss coefficient K, and allowable-loss checks
• Convert round to rectangular and rectangular to round
• View equal-area references alongside equivalent conversions

Built for practical HVAC work:

• Imperial and metric defaults
• Airflow units including CFM, CFS, m³/s, L/s, and m³/h
• Velocity, dimension, length, temperature, friction, and pressure unit controls
• Fractional inch support for dimensions
• Material presets, including flexible duct options with correction support
• Local settings persistence on device

When you need more than a quick answer, engineering detail stays visible. The app can show Reynolds number, Darcy friction factor, dynamic pressure, hydraulic diameter, equivalent round diameter, air density, and dynamic viscosity, so you can see the values behind the result instead of treating it like a black box.

Engineering details include:

• Reynolds number
• Darcy friction factor
• Dynamic pressure
• Hydraulic diameter
• Equivalent round diameter
• Air density
• Dynamic viscosity

Air Duct Size Calculator is intentionally focused on duct sizing, duct analysis, pressure-drop workflow, and equivalent conversion. It is not presented as a full network design suite, report export tool, fitting database, or cloud project system.

If you