Specific Gravity (relative density) calculator


Type of fluid
Specific Gravity


    Liquids and solids

Specific gravity (also called relative density) is the ratio of the density ( ρ ) of a substance to the density of another reference substance at a given specified conditions:
    SG = ρ / ρ reference
Specific gravity for liquids and solids is usually measured with respect to water at 4ºC (or 39.2ºF). Density of water at 4ºC is 1000 kg/m3 or 1 g/cm3.


Specific gravity of gases is defined by:
    SG = Molecular Weight of Gas / Molecular Weight of Standard Air
    (Molecular weight of dry air is 28.96469)

whereas relative density is:
    ρr= Density of Gas / Density of Air (at the same temperature and pressure)
For gases the reference usually is air at room temperature (20ºC or 68ºF) and a pressure of 101.325 kPa absolute. Density of air at 20ºC and 1 atm (101.325 kPa) is 1.205 kg/m3.

If compressibility factors are not considered: ρr= SG.