# Darcy Friction Factor

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Darcy friction factor, abbreviated as $$f_d$$, a dimensionless number, is also known as Darcy-Weisbach friction factor, Darcy friction factor formulas are equations that help calculate the friction losses in pipe flow and open channel flow. This coefficient is used in the Darcy-Weisbach equation.

Fanning friction factor is not the same as the Darcy friction factor.  It is equal to 1/4 the Darcy friction factor.  Since they are basically the same, you need to note which one is being used when doing calculations.  Use fF or fd for the Fanning or Darcy friction factor, respectively.

### Darcy friction factor FORMULA

$$\large{ f_d = \frac { 2 \; h_l \; d \; g } { l \; v^2 } }$$

Where:

$$\large{ f_d }$$ = Darcy friction factor

$$\large{ h_l }$$ = head loss

$$\large{ v }$$ = mean flow velocity

$$\large{ g }$$ = gravitational acceleration

$$\large{ d }$$ = pipe diameter (ID)

$$\large{ l }$$ = pipe length