The study investigates the reduction in masonry walls' strength with different opening sizes and aspect ratios using simplified micro modeling. Calibration of the numerical wall model was done by following an existing wall model from the literature. Springs (COMBIN39) were used to model the compression and shear strength of mortar, whereas contact elements (CONTA178) were used to model the bond between mortar and bricks. The load was provided in two phases; first, the gravity load was applied in the vertical direction to compress the wall then the lateral load was applied. Five walls with an opening size 0%, 1.85%, 3.66%, 10.91%, and 16.5% of the total wall area have been modeled in this study. The analysis results showed that up to an opening area of 4% masonry wall showed approximately 50% reduction in strength and stiffness. Beyond 4% opening size, strength and stiffness drop almost linearly. Such modeling can save cost, time, and know beforehand the type of failure of a masonry wall to avoid life loss.