It is generally recognized that crystal particles’ edges have extra energies that are especially important to small nanoparticles and are responsible for shape transitions during post-nucleation growth of nanoparticles. Edge energies are, however, largely unknown and difficult to measure or compute. In this study, we evaluate contributions of edge energies to formation energies of nanoparticles and propose an effective method for calculating edge energies from observed morphologies. The input parameters are crystal symmetry and fractional surface areas, all of which are experimentally accessible. This method is tested for two typical morphologies of nanocrystals of the cubic crystal system and compared with results computed with the density functional theory. It is thus a practical tool to enrich thermodynamic data of nanomorphologies based solely on experimental observations.