The density of a material is defined as the mass per unit volume.
The units are = kilograms/meter3 = kg/m3 It’s a measure of how tightly the atoms of a material are packed. It has nothing to do with the hardness of the material.
The pressure, P, is defined as the ratio of force to area:
The units of pressure are: Newtons/meter2 = N/m2 = Pascals = Pa