According to Darcy's formula, the loss of head due to friction in the pipe is (where f = Darcy's coefficient, l= Length of pipe, v= Velocity of liquid in pipe, and d=Diameter of pipe)

In fluid dynamics, the Darcy–Weisbach equation is an empirical equation, which relates the head loss, or pressure loss, due to friction along a given length of pipe to the average velocity of the fluid flow for an incompressible fluid. The equation is named after Henry Darcy and Julius Weisbach.