Free Online Manning Pipe Flow Calculator

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Manning Formula Uniform Pipe Flow at Given Slope and Depth

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Flow depth, y Flow depth, y X
Flow area, a Flow area, a X
Pipe area, a0 Pipe area, a0 X
Relative area, a/a0 Relative area, a/a0 X
Wetted perimeter, Pw Wetted perimeter, Pw X
Hydraulic radius, Rh Hydraulic radius, Rh X
Top width, T Top width, T X
Velocity, v Velocity, v X
Velocity head, hv Velocity head, hv X
Froude number, F Froude number, F X
Average shear stress (tractive force), tau Average shear stress (tractive force), tau X
Flow, Q (See notes) Flow, Q (See notes) X
Full flow, Q0 Full flow, Q0 X
Ratio to full flow, Q/Q0 Ratio to full flow, Q/Q0 X


This is the flow and depth inside an infinitely long pipe.
Getting the flow into the pipe may require significantly higher headwater depth. Add at least 1.5 times the velocity head to get the headwater depth or see my 2-minute tutorial for standard culvert headwater calculations using HY-8.

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