Electromagnetic interference filters are broadly used in power electronic systems in order to respect electromagnetic compatibility normative constraints, which considerably increase overall cost and volume mainly because of the common-mode (CM) inductor. In this paper, a new method to calculate the optimal volume of the CM inductor is proposed. It takes into account core saturation issues that may greatly impact inductor volume and filter performances. Consequently, it is shown that in some cases, increasing the inductance value up to the best value can significantly reduce the filter volume in addition to further enhancing the filter attenuation. It is also shown that different nearly-best inductor geometrical parameters with different shape factors can be obtained, which provides an important degree of freedom to designers while introducing the filter in the energy conversion system.