How do you calculate pressure drop using the equivalent length method?

The equivalent length method converts fitting losses to equivalent straight pipe lengths: Le = K*D/f, where K is fitting K-factor, D is diameter, and f is friction factor. Total equivalent length = straight pipe length + sum of fitting equivalent lengths. Pressure drop is then calculated using Darcy-Weisbach for total equivalent length. Alternative: use K-factors directly with dP = K*(rho*v^2/2). The method simplifies calculations but assumes constant friction factor - adequate for most engineering applications.