Determine the hydraulic radius for various channel cross-sections.
Cross-Section dimensions
Calculation Results
Enter dimensions to calculate
About this calculator
Quick Reference
Rh (Rectangular)(b*y) / (b + 2y)
Rh (Circular Full)D / 4
Manning's EqV = (1/n) * Rh^(2/3) * S^(1/2)
Chezy FormulaV = C * sqrt(Rh * S)
Overview
The hydraulic radius (Rh) is the ratio of the cross-sectional area of flow (A) to its wetted perimeter (P). It is a key parameter in Manning's equation for calculating flow velocity.
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Pro Tips
For a circular pipe flowing full, the hydraulic radius is exactly one-fourth of the diameter.
A larger hydraulic radius means less frictional resistance from the channel walls.
In rectangular channels, Rh = (b*y) / (b + 2y).
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Fun Facts
"Despite the name 'radius', Rh is not a physical radius but a ratio of area to boundary length."
"The 'best' hydraulic section is the one with the smallest wetted perimeter for a given area."
"Natural rivers often adjust their shape to optimize their hydraulic radius."
