This method is for determining the piece density (mass per unit volume) of particulate solids by mercury displacement. The method is applicable to catalyst supports and granular material ranging in size from 0.6 mm (30 mesh) to 5 mm (3 mesh) or powders in the range of 0.6 mm to 0.15 mm (100 mesh). Void space between particles is not included in the volume. Internal pores having diameters less than approximately 12 μ,m are included in the volume, larger pores are not. The piece density is reported as g/mL.