In this study, pulsating laminar flow in a pipe is considered numerically. The focus is concentrated on the hydrodynamical development length. At first, steady flow in a pipe is examined and a new correlation for the hydrodynamical development length is developed based on the scale analysis. Then, the pressure-driven pulsating flow is studied. For a constant value of Reynolds number, the effect of the frequency, F and the amplitude, A of the pulsating flow on the development length are determined. It is shown that F for its range of 1 <= F <= 10 dramatically affects the hydrodynamical development length while this effect becomes negligible either for very high values of F (F >= 100) or for low values of F (F <= 0.1). It is also disclosed that the amplitude, A, has a considerable effect on the entrance length for lower values of F (F <= 0.1). For some specific cases, results obtained are compared with those available in the open literature and a good agreement is obtained.