Manning Equation Calculator
Calculate open-channel flow rate and velocity for rectangular, trapezoidal, and circular cross-sections
Manning Equation Calculator
Q = (1/n) · A · R^(2/3) · S^(1/2) · V = Q/A
e.g. 0.001 = 1 m drop per 1000 m length
Results — Rectangular 2.000m × 1.000m
Flow Rate Q
3.0648 m³/s
3064.78 L/s
Mean Velocity V
1.5324 m/s
Cross-section Area A
2.0000 m²
Hydraulic Radius R
0.5000 m
Wetted Perimeter P
4.0000 m
Formula
Q = (1/0.013)·2.0000·0.5000^(2/3)·√0.001
= 3.0648 m³/s
How to Use This Calculator
Enter your input values
Fill in all required input fields for the Manning Equation Calculator. Most fields include unit selectors so you can work in your preferred unit system.
Review your inputs
Double-check that all values are correct and that you have selected the right units for each field. Incorrect units are the most common source of calculation errors.
Read the results
The Manning Equation Calculator instantly computes the output and displays results with units. All calculations happen in your browser — no loading time and no data sent to a server.
Formula Reference
Manning Equation Calculator Formula
See calculator inputs for the governing equation
Variables: All variables and their units are labeled in the calculator interface above.
When to Use This Calculator
- •Use the Manning Equation Calculator when solving homework or exam problems that require quick numerical verification of your hand calculations.
- •Use it during the design phase to rapidly iterate on parameters before running detailed finite element simulations.
- •Use it when reviewing a colleague's calculation or checking a vendor's data sheet for plausibility.
- •Use it to generate reference data for a technical report or presentation without manual computation.
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