This study presents an innovative method for the selection and design of magnetic cores for DC-DC converters. In contrast to conventional approaches that rely on the Area Product ( ) and involve extensive trial and error, our proposed methodology employs two main key parameters: the Core to Copper Loss Ratio (γ) and the Window Utilization Factor ( ) during the inductor design process. Loss models for the inductor are developed based on these variables, taking into account the influence of DC bias, a critical factor in high magnetic field strength applications. To reduce magnetic loss, we utilize the PSO algorithm. The simulation results confirm the effectiveness and rationality of our magnetic models and optimization approach. Therefore, our method offers an efficient and practical alternative to the traditional trial-and-error method for magnetic core selection and design in DC-DC converters