Manning Equation Calculator
Estimate open-channel and partially full pipe flow using Manning equation.
Engineering Calculator
Manning Equation Calculator
Estimate open-channel flow, partially full circular pipe flow, velocity, wetted area, hydraulic radius, Froude number, and boundary shear stress.
Results
Equation used
V = k/n × R2/3 × S1/2
Q = A × V
Typical Manning n starting values
| Surface / channel condition | Typical n |
|---|---|
| Smooth plastic pipe | 0.009–0.011 |
| Concrete pipe or concrete-lined channel | 0.012–0.015 |
| Corrugated metal pipe | 0.022–0.027 |
| Earth channel, clean and straight | 0.020–0.030 |
| Natural stream, clean but winding | 0.035–0.050 |
| Vegetated or rough natural channel | 0.050+ |
What this calculator does
This tool estimates steady uniform flow properties for common channel shapes and partially full circular pipes.
Inputs explained
- Shape: Select the channel or pipe section.
- Geometry: Enter dimensions such as depth, width, diameter, or side slope.
- Slope: Enter the channel or energy grade slope.
- Manning n: Enter the roughness coefficient for the surface condition.
Limitations
Results are based on steady, uniform flow. This tool does not evaluate backwater, controls, hydraulic jumps, rapidly varied flow, sediment transport, scour, culvert inlet control, or tailwater.
FAQ
What is Manning equation used for?
It is commonly used to estimate open-channel flow and gravity flow in pipes when the flow is not pressurized.
What is hydraulic radius?
Hydraulic radius is flow area divided by wetted perimeter.
Can this be used for concrete channels?
Yes, for early checks when the roughness coefficient and geometry are appropriate.
Can this replace a hydraulic model?
No. Use HEC-RAS, SWMM, WSPG, or other required tools for detailed analysis.
Related tools
Need help reviewing this result?
Use this calculator for planning-level checks, then request help if you need a second look at assumptions, units, stormwater criteria, pump sizing, storage volume, or report-ready calculations.