Flow rate
Q = (1/n) A R^(2/3) S^(1/2)
Fluid dynamics calculator
Manning's Equation Calculator
Calculate discharge from area, hydraulic radius, slope, and roughness.
Calculator
Enter values
Choose units beside each input. Results update automatically.
Result
About this calculator
How it works
Manning's equation estimates uniform open-channel flow from roughness and channel geometry.
Formulas
Formulas used
Guide
How to use this calculator
- Enter the known flow, geometry, or fluid property values.
- Select the units beside each input where a unit menu is shown.
- Read the highlighted result first, then use the table for supporting values.
Reference
What the results mean
Flow rate
Estimated open-channel discharge for the entered conditions.
FAQ
Manning's Equation Calculator questions
Can I use different units?
Yes. Select the unit beside each input. The calculator converts values internally before solving.
Are these results suitable for final design?
Use results for education, screening, and early design checks. Verify final work against standards, codes, and project requirements.
Why do fluid results depend so much on assumptions?
Fluid calculations depend on geometry, roughness, density, viscosity, coefficients, and flow regime. Use representative input values and confirm assumptions.
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