Ideal metallic glasses are the metallic glasses that satisfy electronic structure stability. Previously we have developed a so-calledcluster-plus-glue-atom modeland more recently acluster-resonance modelfor the ideal metallic glasses. Good metallic glass forming compositions always satisfy simple cluster formulas cluster (glue atoms), with x denoting the number of glue atoms matching one cluster. In this paper we present an electrochemical potential equilibrium criterion based on these models to obtain the number of glue atoms. By examples of Cu-Zr and Co-B bulk metallic glasses, it is confirmed that the experimentally determined good BMG-forming compositions well agree with the calculated composition formulas.