Culvert Capacity Calculator
Screen a full circular culvert with Manning flow using diameter, slope and roughness.
Use the Culvert Capacity Calculator
Screen a full circular culvert with Manning flow using diameter, slope and roughness.
Calculations happen locally in your browser. ToolLott does not send these inputs to a server for this tool.
Preliminary quantity or geometry estimate only. Confirm dimensions, product data, design requirements, site conditions and project allowances before procurement or construction.
How to use it
Replace the worked-example values with the actual project inputs. Review the intermediate quantities and assumptions before using the result elsewhere.
How the Culvert Capacity Calculator works
This calculator screens full circular flow with Manning’s equation and keeps the boundary between this screen and detailed hydraulic design explicit.
Manning full-flow relation for a circular conduit
The production engine evaluates Q = (1/n) A R^(2/3) S^(1/2). Diameter is converted to metres, slope percent to decimal energy slope, full circular area is A = πD²/4 and hydraulic radius is R = D/4.
Worked example
For D = 0.9 m, S = 0.01 and n = 0.013, the full-flow Manning capacity is approximately 1.81 m³/s and mean velocity approximately 2.846 m/s.
Limitations
This is a preliminary full-flow screening calculation, not a complete inlet-control, outlet-control, headwater, tailwater, debris, scour or final engineering design check.