We propose a generic method to calculate the optical functionalities of a 3D display with a lenticular lens array. In the present work, based on the geometrical optics, it is designed considering the specifications of the display panel. For the effective simulation, we first calculate the optical functionalities of a single cylindrical lens and, by comparing with the results obtained from the conventional geometrical optics, confirm the validity of the present method. Afterwards, we obtain the full distribution of the light intensity at an optimum viewing distance by expanding the results of the single lens to the horizontal plane of the display panel. From these results, we finally confirm whether the 3D images are realized or not in the system.