Theoretical density is an important parameter used to estimate the porosity of materials after sintering, especially if the requirements for the materials’ densities are strict, such as in the case of the parts of solid oxide fuel cells.In this research paper, we provide examples of theoretical density calculations using unit cell structure and X-ray diffraction determined lattice parameters for a number of different ceramics, which are important for energy applications.Oxide perovskites, fluorites and rock salts were all investigated.