Manning’s Equation Calculator

About the Manning’s Equation Calculator

The Manning’s Equation Calculator is a free online tool for engineers, students, and hydraulic professionals to calculate flow rate (Q), flow velocity (V), cross-sectional area (A), or hydraulic radius (R) in open channels, ditches, and streams. By entering the channel slope, Manning’s roughness coefficient (n), and either cross-sectional area or hydraulic radius, the calculator can automatically compute the missing parameter and provide accurate hydraulic flow calculations.

What You Can Calculate

• Flow Rate (Q): Volume of fluid passing through a channel per unit time (m³/s).
• Flow Velocity (V): Average velocity of fluid in the channel (m/s).
• Cross-Sectional Area (A): Compute or input area for hydraulic calculations (m²).
• Hydraulic Radius (R): Ratio of cross-sectional area to wetted perimeter (m).
• Open Channel Design: Optimize slope, roughness, and channel geometry for efficient water transport.

Formulas Used in the Calculator

• Q = (1/n) × A × R^(2/3) × S^(1/2)
• V = Q / A
• Where:
• Q = flow rate (m³/s)
• V = flow velocity (m/s)
• A = cross-sectional area (m²)
• R = hydraulic radius (m)
• S = channel slope (m/m)
• n = Manning’s roughness coefficient (dimensionless)

How to Use the Calculator

1. Enter the channel slope (S) as a dimensionless ratio (m/m) or percent.
2. Provide the Manning’s roughness coefficient (n) based on channel material.
3. Enter either cross-sectional area (A) or hydraulic radius (R). Leave the other blank to compute it automatically.
4. The calculator instantly displays the flow rate (Q), flow velocity (V), and the missing parameter.

Applications of Manning’s Equation

Manning’s equation is essential in hydraulic engineering for designing and analyzing open channels, rivers, irrigation ditches, and streams. Engineers use it to predict water flow, optimize channel geometry, reduce erosion, and ensure efficient and safe hydraulic system performance.