Specific gravity is a measure that compares the density of a substance to the density of water. It is a dimensionless quantity, meaning it has no units. If a substance has a specific gravity less than 1, it will float in water, while a specific gravity greater than 1 indicates that it will sink. To calculate specific gravity, you divide the density of the substance by the density of water at a specific temperature, usually 4°C, where water is most dense. This property is useful in various fields, including geology, engineering, and chemistry, for identifying materials and assessing their behavior in different environments.