Current guidelines such as TM5 and ASCE use a trial and error procedure to design RC slabs against blast loads. Although the trial and error procedure is easy to implement, it may not result in a optimal to resist blast loads. In this study, SDOF system recommended by TM5 and ASCE was adopted to simplify RC slabs; the bilinear model was selected to simulate the resistance-deflection curve for dynamic response analysis. After comparing the areas under the resistance-deflection curves of RC slabs with different reinforcement ratios, the reinforcement ratio responding to the biggest area can be defined as the optimal reinforcement ratio. These derived relationships are useful to facilitate a design with maximum capacities to resist blast loads.