The Darcy–Weisbach friction factor f D is 4 times larger than the Fanning friction factor f, 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 f D is more commonly used by civil and mechanical engineers, and the Fanning factor f by chemical engineers, but care should be taken to identify the correct factor regardless of the source of the chart or formula.