Duct sizing tool.
Check air velocity and straight-duct friction for a circular or rectangular duct. Change a size and compare the result.
Know what
the result includes.
Flow, velocity and friction
Velocity = flow ÷ area. Pressure loss uses Darcy–Weisbach with an iterated Colebrook friction factor for turbulent flow. Rectangular ducts use hydraulic diameter 2ab/(a+b); the result is an engineering approximation, limited here to aspect ratios up to 5:1.
Air properties are fixed at approximately 20°C and atmospheric pressure: density 1.204 kg/m³ and dynamic viscosity 0.00001825 Pa·s. Straight-section losses exclude bends, branches, terminals, leakage, equipment and fan system effects. Noise and available space still need checking. See ASHRAE’s duct-design reference.
Transitional-flow pressure loss and low-Reynolds-number rectangular friction are not estimated. This tool does not select a fan or establish a complete system pressure.
Calculations run in your browser. Engin does not save these inputs.
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