# Darcy friction factor - Goudar–Sonnad equation

## 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 variables (a), (d), (q) and (D_CFA) can be calculated using these formulas.

**See Also:**

Variable (a) formula

Variable (d) formula

Variable (q) formula

Variable (D_CFA) formula

## Variables

f | Darcy friction factor (dimensionless) |

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

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

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

D_{CFA} | Variable in Goudar–Sonnad equation (dimensionless) |