Although the Manning's Equation is most often used for calculating flow in open channels?, it can also be used to calculate flow in pipes.

### Manning's Equation for Circular Pipes:

Q = \frac{1.49}{n}AR^{2/3}\sqrt{S}

*where:*

**A**= cross-sectional flow area (ft^{2})**R**= hydraulic radius (ft)**S**= slope of energy grade line or slope of channel bed for uniform flow**n**= manning roughness factor (see Table of Manning's Roughness Coefficients)

### Head Loss

h_F = \frac{4.637n^2L}{D^{5.333}}Q^2

*where:*

**h**= friction head loss (ft)_{f}**n**= Manning Roughness Coefficients**L**= length of pipe (ft)**Q**= discharge (ft^{3}/sec)**D**= diameter of pipe (ft)