Specific gravity is a ratio that compares the density of a substance to the density of a reference material, usually water.
You can measure specific gravity using a variety of methods, but the easiest method is to divide the weight of the liquid by its volume and use water as the reference since we know the density of water is 1 gram per milliliter (g/mL).
Example:
100 mL of juice weighs 104 grams.
- Calculate its density: 104 g/100 mL = 1.04 g/mL
- Divide the density of the juice by the density of water to get the specific gravity: 1.04 g/mL / 1 g/mL = 1.04. 1.04 is the specific gravity.
- Since this represents a comparison of two different densities, the units cancel out, leaving just the value.