Specific gravity of a substance a comparison of the density of
a substance relative to a standard value. Scientists express specific gravity
of liquids and solids using water at 4^{o}C as the standard.

In calculating the specific gravity of a substance, the density
of the substance and the density of water are expressed in the same units. This
leaves specific gravity unitless.

The density of water at 4^{o}C is 1.00 g/mL. Therefore,
the density of solids or liquids expressed as g/mL is numerically equal to their
specific gravities.

The notation of expressing specific gravity is given below. Place
your mouse over the image to get a brief explanation of the notation.