Hydraulic Radius Calculator
Calculate hydraulic radius R = A / Pw from cross-sectional flow area and wetted perimeter.
How to Use This Calculator
Determine A and Pw
Compute or obtain the cross-sectional flow area and wetted perimeter for your channel or pipe.
Enter values
Enter A (m²) and Pw (m). Ensure both correspond to the same cross-section.
Calculate R
Press Calculate to get hydraulic radius R in meters.
Formula
R = A / Pw
Where: R is hydraulic radius, A is flow area, Pw is wetted perimeter.
Example: A = 3.6 m², Pw = 5.4 m ⇒ R = 0.6667 m.
About Hydraulic Radius Calculator
Hydraulic radius measures the efficiency of a cross-section to convey flow and appears in friction and resistance relations such as Manning and Darcy–Weisbach (for open-channel analogues).
When to Use This Calculator
- Open-channel design: Evaluate section efficiency.
- Comparing shapes: Rectangular vs trapezoidal sections.
- Hydraulic analysis: Feed R into Manning-based discharge estimates.
Why Use Our Calculator?
- ✅ Simple: Directly computes R from A and Pw.
- ✅ Versatile: Works for any cross-section if A and Pw are known.
- ✅ Useful: Integrates with Manning and other hydraulic relations.
Frequently Asked Questions
How do I get A and Pw?
For simple shapes: rectangular A=b·y, Pw=b+2y. For complex shapes, compute based on geometry or use numerical methods.
What are typical units?
Area in m² and perimeter in m yield R in meters. Use consistent units.
Is hydraulic radius the same as hydraulic diameter?
Hydraulic diameter Dh = 4A/Pw (used often for closed conduits). Hydraulic radius is R = A/Pw.