Specific gravity (SG) of a material, a mixture of materials or a clay slip is expressed as how many times it is heavier than the same amount of water, i.e. how many kg per 1 lifer volume or gram per cm³. Density is the weight per volume unit and in the metric system this equals specific gravity (g/cc or kg/l) but in many countries slip densities are still measured in ounces per pint.
The density of a clay slip is found by weighing 1 liter of the slip. If it weighs 1.6 kg the slip has a density of 1.6.