It is shown that the entry flow of a Bingham fluid is not fully developed at the axial position where the center line velocity reaches 99% of the fully developed value, which is the classical definition. Therefore, the entry length of the Bingham fluid is determined based on the newly expanded definition in this study, viz., the axial length where the velocity at the radial position of 95% of plug radius, reaches 99% of the fully developed value. For a power law fluid, the entry length is determined based on the classical definition, In order to obtain the corrected Reynolds number Re*, Ito's method is employed in this study. It is shown that the entry lengths of Newtonian, Bingham and power law fluids are correlated by the same equations in the range of Re* < 20.