In recent years, many soft wearable robots have been developed to overcome the limitations of conventional rigid wearable robots. Among the types of soft robots, soft pneumatic actuators (SPA) have been developed because of compliant characteristics that can guarantee safe human-robot interaction to improve one of the rigid wearable robot limitations. Especially, among various SPAs, inflatable actuators have been developed because they can be easily manufactured with various types of structures. However, the theoretical modelings proposed in the inflatable actuators are specific to apply to other joints, because their purpose is performance analysis. In this paper, we improve the theoretical modeling for the design of wrinkled inflatable actuators. The actuator’s design parameters such as height and number of layers were determined by the proposed theoretical model to provide the target torque. The soft actuator was manufactured with determined design parameters and then measure the torque for the various angles and pressures. The theoretical torque values acquired through the proposed theoretical model have an error of < 8% from the experimental torque values and showed higher accuracy than the previously proposed model.