To draw parallels between quantum mechanical and FEM calculations of permittivity, it is necessary to rigorously define the inclusion volumes. The loading in quantum simulations is defined by atom volumes. Inclusion atoms replace matrix atoms in a one-to-one ratio. This suggests one option, which is to consider the percent atomic loading as a stand-in for volume loading. While this is a sufficient definition when loading is used only as a system descriptor, we find that a more rigorous definition of volume is necessary when developing inclusion shape, size and loading parameters for FEM.