Specific density

Compare density.

Not to be confused with specific weight.

Specific density
Common symbols	$\rho _{sp}$
SI unit	dimensionless
Derivations from other quantities	$\rho _{=}{\frac {\text{m}}{\mathrm {V} }}{\frac {1}{\mathrm {\rho _{ref}} }}$

Definition

Specific density is a now obsolete term for relative density, which is the now preferred term.

Specific density is the density of an object divided by the density of a reference material. Specific gravity, a still-used but deprecated term, is the same as relative density. As an example, if a material has a specific density or relative density or specific gravity of 5, that means it has five times the density of some reference material (which should be named as part of the definition).

Density vs. gravity

Specific density, being the same as relative density, is a dimensionless quantity. Usually specific density is density relative to water, but other types of relative density are possible (such as density relative to the density of dry air).