The interleaved boost converter with coupled inductors which achieves high power density has gained great attention in automotive applications. However, the temperature of the inductor tends to be high because loss density is increased by the high power density. Therefore, it is important to calculate the inductor losses when the inductors in high power density converters are designed. In this paper, firstly, a core loss calculation method for the coupled inductor is proposed. Then, accuracy of the core loss calculation method is confirmed by experimental validation. Finally, magnetic properties of the used cores are shown and then the usefulness of the coupled inductors is discussed from different viewpoints of inductor losses and volume comparing single-phase, two-phase and two-phase converter with coupled inductors methods by using the imaginary inductors theory. As a result, inductor loss of the coupled inductors can be reduced compared to conventional methods, and a superior core material is suggested.