Density is defined as mass per unit volume
1. Crystallographic density: the ideal density of a specific crystal structure calculated from chemical composition data and from inter-atomic spacing data obtained by x-ray diffiraction.
2. Theoretical density: the density of a material that contains zero microstructural porosity(takes into account multiple phases, defect structures, and solid solution).
3. Bulk density: the measures density of a bulk ceramic body (includes all porosity, lattice defect, and phases).
4. Specific gravity: the density of a material relative to the density of an equal volume of water at 4 ๐C (usually based upon crystallographic or theoretical density).