Free Online Manning Pipe Flow Calculator

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Manning Formula Uniform Pipe Flow at Given Slope and Depth

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Solve for y/d₀ given Q — Using d₀, n, and S_f from the calculator form, finds the lowest y/d₀ for a given Q.
Flow, Q:

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Inputs

Pipe diameter, d₀		X
Manning roughness, n		X
Friction slope, S_f?		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
Velocity check	Velocity check		X
Froude number, Fr	Froude number, Fr		X
Average shear stress, τ	Average shear stress, τ		X
Flow, Q ?	Flow, Q ?		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 estimate the headwater depth, or see my 2-minute tutorial for standard culvert headwater calculations using HY-8.