Physics
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Hydraulic Radius Calculator.
Calculate hydraulic radius from wetted area and perimeter.
Set your values
Results update as you type.
Educational SI models with assumptions stated in each description; verify engineering decisions independently.
Use Cases
Open Channel Flow Analysis
Engineers use hydraulic radius to determine flow velocity and capacity in rivers, canals, and culverts. This calculator simplifies the initial calculation for design and analysis.
Example: For a rectangular channel with area 2 m² and wetted perimeter 4 m, hydraulic radius = 0.5 m.
Pipe and Sewer Design
In partially filled pipes, hydraulic radius affects flow characteristics. Use this tool to quickly compute the radius for various fill levels to optimize pipe sizing.
Example: A sewer pipe with wetted area 0.3 m² and perimeter 1.5 m gives hydraulic radius 0.2 m.
Frequently Asked Questions
- What is hydraulic radius and why is it important?
- Hydraulic radius is the ratio of the cross-sectional area of flow to the wetted perimeter. It characterizes the efficiency of a channel or pipe in conveying flow. A larger hydraulic radius indicates higher flow capacity and lower resistance, crucial for designing efficient drainage and irrigation systems.
- How do I use this calculator?
- Simply enter the wetted area (in square meters) and the wetted perimeter (in meters) into the respective fields. The calculator will compute the hydraulic radius by dividing the area by the perimeter, giving you the result in meters.
- What units should I use?
- The calculator expects the wetted area in square meters (m²) and the wetted perimeter in meters (m). The resulting hydraulic radius will be in meters (m). Ensure both inputs are in the same unit system for accurate results.
Tips & Common Mistakes
Tips
- Ensure both inputs are in the same unit system (e.g., meters) to get the hydraulic radius in meters.
- For a circular pipe flowing full, the hydraulic radius equals the pipe radius divided by 2 (R = D/4).
- Use the hydraulic radius to compare flow efficiency between different channel shapes.
- Double-check your measurements: wetted area and perimeter must correspond to the same cross-section.
Common Mistakes to Avoid
- Using diameter instead of radius in the wetted perimeter for circular pipes.
- Mixing units, such as entering area in square feet and perimeter in meters, leading to incorrect results.
- Forgetting that the wetted perimeter excludes the free surface in open channels; only the wetted boundary counts.
Last updated: August 13, 2026