This paper proposes a method for modeling the Center of Mass (CoM) of humanoid robots. The method is based on the Statically Equivalent Serial Chain (SESC) model, a serial chain representation of any multi-link branched chain. An algorithm is presented to automatically construct the SESC of a symmetric anthropomorphic architecture. We also show the use of SESC modeling in the projection of the CoM when the kinematic chain is not positioned on a horizontal plane. Finally, after validating these developments on the HOAP-3 experimental humanoid robot platform, we discuss the interest of this modeling in other areas of research.