Free Online Manning Pipe Flow Calculator

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Manning Formula Uniform Pipe Flow at Given Slope and Depth

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Inputs

Pipe diameter, d₀		X
Manning roughness, n		X
Pressure slope (possibly ? equal to pipe slope), S₀		X
Relative flow depth, y/d₀		X

Results

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, P_w	Wetted perimeter, P_w		X
Hydraulic radius, R_h	Hydraulic radius, R_h		X
Top width, T	Top width, T		X
Velocity, v	Velocity, v		X
Velocity head, h_v	Velocity head, h_v		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

Notes:

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.