Specific gravity

Specific Gravity (SG) is a special case of relative density.

It is defined as the ratio of the density of a given substance, to the density of water (H₂O). Substances with a specific gravity greater than 1 are heavier than water, and those with a specific gravity of less than 1 are lighter than water.

${\displaystyle {\mbox{SG}}={\frac {\rho _{\mathrm {substance} }}{\rho _{\mathrm {H2O} }}}}$ ^[1]

SG is by definition dimensionless and therefore not dependent on the system of units used (e.g. slugsft⁻³ or kgm⁻³), assuming that the units are consistent. Based on the SG-value of a given substance, the density of that substance can be calculated.

1. ↑ The density of the denominator, or reference, is ${\displaystyle \rho _{\mathrm {H2O} }}$ = 1000kgm^-3 (at 4°C/39.2°F) in SI units.