How is hydraulic radius different from hydraulic diameter?

Hydraulic radius is the cross-sectional area of flow divided by the wetted perimeter (A/P), used for open channels; hydraulic diameter is four times the hydraulic radius and is used for flow in non-circular closed conduits.

Can this calculator handle partially filled pipes?

Yes, the tool includes a Pipe (part-filled) option where you input the pipe diameter and the fill depth to determine the wetted perimeter and hydraulic radius for that specific flow depth.

What units should I use for the dimensions?

You can enter dimensions in any consistent unit (meters, feet, inches); the calculator will compute the hydraulic radius in the same unit as the inputs.

Is the hydraulic radius the same as the radius of the pipe?

No, the hydraulic radius is the area divided by the wetted perimeter; for a full circular pipe it equals one-quarter of the pipe's diameter, but for partially filled pipes it is always smaller than the actual radius.

PhysicsFree Tool

Hydraulic Radius Calculator

Provided byOmni Calculatoromnicalculator.com

The hydraulic radius calculator finds the wetted perimeter and hydraulic radius for five different channel shapes.

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Screenshot of Hydraulic Radius Calculator on Omni Calculator — omnicalculator.comOpen the live tool →

About this tool

What Hydraulic Radius Calculator does

The Hydraulic Radius Calculator on Omni Calculator determines the wetted perimeter and hydraulic radius for five common open-channel shapes—rectangular, trapezoidal, triangular, and pipe (full or part-filled)—using user-supplied dimensions. It outputs the cross-sectional area, the length of wall in contact with the fluid, and the resulting hydraulic radius, which is the ratio of area to wetted perimeter. These metrics are essential for analyzing flow characteristics in drainage design, civil engineering, and environmental science projects.

Step by step

How to use the Omni Calculator Hydraulic Radius Calculator

1
Select the channel shape from the Shape dropdown menu
2
Enter the geometric dimensions required for the chosen shape (e.g., width and depth for rectangular, base and side slope for trapezoidal)
3
View the calculated results for cross-sectional area, wetted perimeter, and hydraulic radius displayed instantly
4
Use the Share result or Clear all functions to export or reset the calculation

Is it right for you

Best for

Civil engineers, hydrology students, and anyone designing open channels or pipe flow systems who needs quick, accurate hydraulic radius and wetted perimeter values without manual calculations.

Limitations

Designed for steady, uniform open-channel flow; not suitable for pressurized full pipe systems beyond the fill-level options provided
Assumes simple geometric cross-sections; irregular or natural stream beds require more advanced modeling
Results are based on idealized shapes and may not account for real-world factors like roughness or sediment load

Questions

Hydraulic Radius Calculator FAQ

How is hydraulic radius different from hydraulic diameter?: Hydraulic radius is the cross-sectional area of flow divided by the wetted perimeter (A/P), used for open channels; hydraulic diameter is four times the hydraulic radius and is used for flow in non-circular closed conduits.
Can this calculator handle partially filled pipes?: Yes, the tool includes a Pipe (part-filled) option where you input the pipe diameter and the fill depth to determine the wetted perimeter and hydraulic radius for that specific flow depth.
What units should I use for the dimensions?: You can enter dimensions in any consistent unit (meters, feet, inches); the calculator will compute the hydraulic radius in the same unit as the inputs.
Is the hydraulic radius the same as the radius of the pipe?: No, the hydraulic radius is the area divided by the wetted perimeter; for a full circular pipe it equals one-quarter of the pipe's diameter, but for partially filled pipes it is always smaller than the actual radius.

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