# Darcy Friction Factor

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Darcy friction factor, abbreviated as $$f_d$$, a dimensionless number, also called Darcy-Weisbach 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 $$f_f$$ or $$f_d$$ for the Fanning or Darcy friction factor, respectively.

## Darcy friction factor formula

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

### Where:

 Units English Metric $$\large{ f_d }$$ = Darcy friction factor $$\large{ dimensionless }$$ $$\large{ g }$$ = gravitational acceleration $$\large{ \frac{ft}{sec^2} }$$ $$\large{ \frac{m}{s^2} }$$ $$\large{ h_l }$$ = head loss $$\large{ ft }$$ $$\large{ m }$$ $$\large{ l_p }$$ = lenght of pipe $$\large{ ft }$$ $$\large{ m }$$ $$\large{ v }$$ = mean flow velocity $$\large{ \frac{ft}{sec} }$$ $$\large{ \frac{m}{s} }$$ $$\large{ d }$$ = pipe inside diameter $$\large{ in }$$ $$\large{ mm }$$ 