SIA Engineering Company provides aircraft maintenance, repair and overhaul (MRO) services to more than 80 international and aerospace equipment manufacturers worldwide. Our project aims to develop a model that automatically assigns optimal order quantity Q* and optimal reorder point r* for every single inventory item. We used Q-Q plot to visualize and Wilk-Shapiro test to determine numerically if the demand distribution is normally distributed for the data. We also calculated 95% confidence interval for our mean demand so that we can be confident that on average we are able to meet demand during the 1 month of supply lead time. We modeled the inventory with (Q,r) model and evaluated using fill rate as one of the performance measures.