Three-phase common mode (CM) inductors are widely used in electric motor drives as a means to limit ground current, shaft voltage, and electromagnetic interference emission. As the switching frequency of power converters keeps increasing with the help of high performance switching devices such as SiC MOSFETs, the role of CM inductors are becoming increasingly important. This paper presents a comprehensive analysis on the magnetic design and sizing of three-phase CM inductors. Analytical calculation of critical parameters such as leakage inductance, stray capacitance, flux density, and losses will be addressed in the paper. Design constraints that determine the size of magnetic cores will also be shown. Finally, a systematic design procedure that minimizes the CM inductor size will be proposed and verified.