Tests involving the Classical Nucleation Theory (CNT) often disregard the size dependence of surface energy. Thus, the surface energy of critical nuclei is assumed to be a macroscopic quantity that depends only on the temperature of a flat surface. However, because the size of critical nuclei changes with temperature, σcl(T) should be described as a function of both temperature and size of critical nuclei. The present work examines the temperature dependence of macroscopic surface energy, decoupling it from the size dependent part. Tolman, Rasmussen and Vogelsberger's equations are used to decouple the dependence of surface energy on size, using experimental data for the following silicate glasses Li2O.2SiO2 (LS2) and Na2O.2CaO.3SiO2 (N1C2S3). These equations are successful in obtaining a decrease in σcl(T), in agreement with theoretical predictions. For all the values of δ , Tolman's equation produces the lowest values of σcl(T). Nevertheless, they are very close to the liquid/vapor surface energy (σlv), which contradicts the Stefan's rule (i.e. σcl/σ lv << 1). Therefore, it is demonstrated that the assumption of the curvature dependence of surface energy does not suffice, per se, to explain the discrepancy between the experimental and theoretical values of nucleation rates.