Use this engineering calculation for a transparent preliminary estimate or independent arithmetic check when geometry, materials, loads, operating conditions, and units are defined consistently.

Manning N

Required number input.

Area Square Meters (m²)

Required number input.

Hydraulic Radius Meters (m)

Required number input.

Slope

Required number input.

Open-channel discharge from Manning n, flow area, hydraulic radius and energy slope in SI units. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Flow Cubic Meters Per Second (m³/s)

The resulting flow cubic meters per second returned as a number.

• Hydraulic equations require consistent datum, fluid properties, geometry, roughness, flow regime, and loss coefficients. Cavitation, air entrainment, unsteady flow, fittings, sediment, free-surface effects, and pump behavior may require a network or numerical model.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check assumptions against drawings, measurements, current material data, and the applicable design code. Apply required load combinations and safety factors, then obtain qualified review and testing for consequential designs.

• Manning Velocity

  Open-channel mean velocity from Manning n, hydraulic radius and energy slope in SI units.

• Chezy Coefficient

  Chezy velocity coefficient derived from Manning roughness and hydraulic radius in SI units: C=R^(1/6)/n.

• Critical Depth Rectangular

  Critical depth of rectangular open-channel flow from unit-width discharge q: yc=(q²/g)^(1/3).