In British brewing practice, the specific gravity, as specified above, is multiplied by 1000. Temperatures for both sample and reference vary from industry to industry.
Where it is not, it is more usual to specify the density directly. Pressure is nearly always 1 atm (101.325 kPa). Temperature and pressure must be specified for both the sample and the reference. A substance with a relative density greater than 1 will sink. For example, an ice cube, with a relative density of about 0.91, will float. If the reference material is water, then a substance with a relative density (or specific gravity) less than 1 will float in water.
If the relative density is exactly 1 then the densities are equal that is, equal volumes of the two substances have the same mass. If a substance's relative density is less than 1 then it is less dense than the reference if greater than 1 then it is denser than the reference. or RD) is often preferred in scientific usage, whereas the term "specific gravity" is deprecated. The term "relative density" (often abbreviated r.d. Specific gravity for liquids is nearly always measured with respect to water at its densest (at 4 ☌ or 39.2 ☏) for gases, the reference is air at room temperature (20 ☌ or 68 ☏). Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material.
A United States Navy Aviation boatswain's mate tests the specific gravity of JP-5 fuel