Fanning and Moody friction factors

What is the difference ?

How to calculate Moody factor from Fanning factor ?

1. Introduction
2. Relation in between Fanning and Moody friction factors

1. What is the difference in between Fanning and Moody friction factors ?

The friction factor is used to calculate the pressure drop due to the flow of a fluid in a pipe. It represents the interaction in between the fluid and the pipe. One must be extremely careful when consulting literature for correlations as the nature of the friction factor used in not always very well apparent. It can indeed be expressed according to Moody or to Fanning, with a factor 4 in between both coefficients.

Pipe friction coefficient according to Moody and Fanning

Figure 1 : Friction at the pipe interface

2. Relation in between Fanning and Moody friction factors

Moody factor can be calculated from Fanning factor with the following formula :

**f_Moody = 4*f_Fanning**

f_Moody = Moody's friction factor

f_Fanning = Fanning's friction factor

Note that Moody's friction factor is sometimes called Darcy or Darcy-Weisbach friction coefficient.

Fanning or Moody friction factors can be calculated thanks to abacus (Moody diagram for example) or correlations, for example the Churchill correlation.

Moody diagram calculation friction factor