# Darcy friction factor - Goudar–Sonnad equation (Variable b)

## Description

In fluid dynamics, the Darcy friction factor formulae are equations that allow the calculation of the Darcy friction factor, a dimensionless quantity used in the Darcy–Weisbach equation, for the description of friction losses in pipe flow as well as open-channel flow.

The Darcy friction factor is also known as the Darcy–Weisbach friction factor, resistance coefficient or simply friction factor; by definition it is four times larger than the Fanning friction factor.

Goudar equation is the most accurate approximation to solve directly for the Darcy–Weisbach friction factor f for a full-flowing circular pipe. It is an approximation of the implicit Colebrook–White equation.

The shown formula calculates the variable (b) in Goudar–Sonnad equation. The variable (b) is not directly substituted in the Goudar–Sonnad equation, instead, it’s used to calculate the variables (s) and (g)

**See Also:**

Variable (s) formula

Variable (g) formula

## Variables

b | Variable in Goudar–Sonnad equation (dimensionless) |

ϵ | Pipe's effective roughness height (m) |

D | Pipe's inside diameter (m) |