# Specific Gravity (relative density) calculator

## Calculator

## Theory

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:

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/m

^{3} or 1 g/cm

^{3}.

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:

ρ_{r}= 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/m

^{3}.

If compressibility factors are not considered: ρ

_{r}= SG.

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