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

## 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 (a) in Goudar–Sonnad equation

**See Also:**

Goudar–Sonnad equation formula

Related formulas## Variables

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