The Darcy–Weisbach friction factor  is 4 times larger than the Fanning friction factor , so attention must be paid to note which one of these is meant in any "friction factor" chart or equation being used. Of the two, the Darcy–Weisbach factor  is more commonly used by civil and mechanical engineers, and the Fanning factor  by chemical engineers, but care should be taken to identify the correct factor regardless of the source of the chart or formula.
Note that
Most charts or tables indicate the type of friction factor, or at least provide the formula for the friction factor with laminar flow. If the formula for laminar flow is , it is the Fanning factor , and if the formula for laminar flow is , it is the Darcy–Weisbach factor .
Which friction factor is plotted in a Moody diagram may be determined by inspection if the publisher did not include the formula described above:
#Observe the value of the friction factor for laminar flow at a Reynolds number of 1000.
#If the value of the friction factor is 0.064, then the Darcy friction factor is plotted in the Moody diagram.  Note that the nonzero digits in 0.064 are the numerator in the formula for the laminar Darcy friction factor: .
#If the value of the friction factor is 0.016, then the Fanning friction factor is plotted in the Moody diagram.  Note that the nonzero digits in 0.016 are the numerator in the formula for the laminar Fanning friction factor: .
The procedure above is similar for any available Reynolds number that is an integer power of ten.  It is not necessary to remember the value 1000 for this procedure—only that an integer power of ten is of interest for this purpose.