# Manning formula

## Description

The Manning formula is also known as the Gauckler–Manning formula, or Gauckler–Manning–Strickler formula in Europe. In the United States, in practice, it is very frequently called simply Manning’s Equation. The Manning formula is an empirical formula estimating the average velocity of a liquid flowing in a conduit that does not completely enclose the liquid, i.e., open channel flow. All flow in so-called open channels is driven by gravity.

Related formulas## Variables

V | Cross-sectional average velocity (in m/s) (dimensionless) |

k | Conversion factor (1 for SI units system , k=1.49 for English units) (dimensionless) |

S | The linear hydraulic head loss ( the same as the channel bed slope when the water depth is constant) (dimensionless) |

A | Cross sectional area of flow (in m^2) (dimensionless) |

P | Wetted perimeter of cross-sectional flow area (in m) (dimensionless) |

n | Gauckler–Manning coefficient (in s/m^1/3) (dimensionless) |