: One of the main problems with the design of pillars in room and pillar mines is the design of pillars with a high safety factor to ensure their stability, leading to the loss of much of the ore resulting in financial damage to the project. Therefore, it is necessary to use a method for evaluation of pillar stability in different ratios of width to height and optimization of pillar dimensions. The purpose of this study is to investigate the stability of pillars with different ratios of width to height in different geomechanical conditions and to provide a solution to optimize the dimensions of pillars in room and pillar mines. The physical and mechanical properties of the ore, hanging wall and foot wall have been collected from three studies in this field. Using numerical modeling in FLAC3D software, the stress, displacement and plastic zone contours were obtained for different ratios of width to height and different geomechanical conditions as well as the maximum stresses at the pillar. The values of vertical stress, horizontal displacement, vertical displacement and percentage of plastic zone were compared in different conditions. Also, the maximum stresse at the pillar were compared with the experimental equations of the pillar strength evaluation to evaluate their stability under different conditions. Numerical modeling results show that by increasing the rock mass modulus, the plastic zone at the pillar decreases by 28% for w/h=1, and increases with the w/h ratio to about 40%. The comparison between the modeling results and the analytical methods shows that due to the rock mass quality and considering the Value of rock modulus and also the width of the stope in hard rocks for 2 w/h 1 shows good stability. On the other hand, the comparison of maximum stresses based on the experimental equations showed that by increasing the rock strength, the width of the pillar can be reduced to lower values and more ore extraction. Therefore, according to the geomechanical conditions of the area, the ratio of width to height of the pillar must be chosen so that while controlling the pillar instability, the lowest possible amount of mineral remains in-place.