A modification of the reinforcement formula that considers the realistic frictional characteristics of subbase types is presented. The objective of this study is not to abandon the current formula but to arrive at a better formula, one that considers the field observations. Rational reinforcement design is important because the amount of reinforcement affects the restraint on the movement of a pavement section, or slab, and the long-term performance. This study was the result of a need to revise the reinforcement formula based on the subbase drag theory. The reinforcement formula was modified in accordance with the experimental results obtained concerning subbase frictional resistance. The modification was necessary to include the actual characteristics of subbase friction in the reinforcement design formula for both continuously and jointed reinforced concrete pavements. The new formula reflects the experimental results concerning subbase friction. It represents the actual components of frictional resistance at the interface: adhesion, bearing, and shear. The implementation of information from this study will result in more rational reinforcement design. The formula calculates the steel requirement for the middle of the slab; in other words, the calculated value is the maximum requirement, and the locations between the free end and the middle of the slab will require less reinforcement. Further experimental study is necessary to calibrate the new formula.