# Darcy friction factor - Swamee–Jain 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.

The Swamee–Jain equation is used 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.

Related formulas## Variables

f | Darcy friction factor (dimensionless) |

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

D | Pipe's inside diameter (m) |

Re | Reynolds number (dimensionless) |