Manning Equation Calculator
Enter channel geometry, slope, and Manning's roughness coefficient to compute flow velocity and discharge.
Channel Parameters
Results
Velocity (V)
—
m/s
Discharge (Q)
—
m³/s
Flow Area (A)
—
m²
Hydraulic Radius (R)
—
m
Formula Used
Fill in the parameters on the left and click Calculate.
Common Manning's n Values
| Material | n Range |
|---|---|
| Smooth concrete | 0.010–0.013 |
| Concrete pipe | 0.012–0.015 |
| Corrugated metal pipe | 0.013–0.024 |
| Earth channel (clean) | 0.018–0.025 |
| Gravel/cobble | 0.025–0.040 |
| Natural stream | 0.025–0.075 |
Summary
Enter channel geometry, slope, and Manning's roughness coefficient to compute flow velocity and discharge.
How it works
- Select a channel cross-section shape (rectangular, trapezoidal, circular, or triangular).
- Enter the channel dimensions and flow depth in the fields that appear.
- Input the longitudinal bed slope as a dimensionless ratio (e.g., 0.001 for 1 in 1000).
- Select or enter the Manning's roughness coefficient n for your channel material.
- Choose unit system (metric or US customary) and click Calculate.
- Velocity (V), discharge (Q), hydraulic radius (R), and flow area (A) are shown instantly.
Use cases
- Size storm drains and culverts for drainage design.
- Estimate river or stream discharge for flood routing.
- Verify flow capacity of irrigation ditches and canals.
- Design roadside swales and trapezoidal channels.
- Check existing channel capacity against design storm runoff.
- Compute normal depth for a given discharge in hydraulic studies.
Frequently Asked Questions
Last updated: 2026-07-24 ·
Reviewed by Nham Vu