Model based controllers are widely used to control motions of humanoid robots. In most cases these are based on the center of mass (CoM) model of the humanoid. For this it is important that the parameters of this model are accurately known. In this paper we contribute a method to estimate the base parameters of the full 3D CoM model of humanoid robots. This method only uses measurements of the joint angles and static contact forces for a number of postures. We also contribute a method to determine optimal stable measurement postures. The estimation method is verified in experiments on humanoid robot TUlip and a statistical analysis is performed to check the reliability of the estimated base parameters.