Cranes are designed for lifting, moving heavy loads in factories, workshops or in ports, they require a high level of safety and reliability. Therefore, ensuring durability is not enough for the calculations and design of the crane. This paper solves the optimal design problem of double girder overhead crane based on reliability. A crane model shall be built in double girder structure, closed rectangular box shape cross section, the rail trolley shall be considered to be a portable load in which a pendulum type load is suspended. We have built the oscillating differential equations, the force equation, the moment equation, and the deflated equation, from there, determined the maximum forces and moments placing on the beam. We used strength conditions to determine the cross-sectional area of the girders. The factors of safety fs = 1.5, fs = 2.0, and fs = 2.5 produces the result of As = 8156.52 mm2, As = 9410.94 mm2, and As = 10516.14 mm2 respectively. Then we used mathematical statistics to determine the cross-sectional area according to the reliability, the result is As = 8362.08 mm2 corresponding to the factor of safety fs = 1.58. The achieved results show that when calculated under durable conditions, the factor of safety is often selected based on the experience of the designer. Therefore, it is not possible to calculate the risks occurring during the long operation time of the crane, causing economic and human costs. In this study, we have overcome the disadvantages to ensure the reliability of the crane structure with the optimal size