Free Online Manning Pipe Flow Calculator

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Manning Formula Uniform Pipe Flow at Given Slope and Depth

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 (sometimes ? equal to pipe 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 (tractive force), τ	Average shear stress (tractive force), τ	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 estimate the headwater depth, or see my 2-minute tutorial for standard culvert headwater calculations using HY-8.