Specific Gravity (Relative Density)

 

 

 

Specific Gravity - SG - is a dimensionless unit defined as the ratio of the density of a substance to the density of water - at a specified temperature, and can be expressed as

SG = ρ_substance / ρ_H2O         (3)

where

SG = Specific Gravity of the substance

ρ_substance = density of the fluid or substance (kg/m³)

ρ_H2O = density of water - normally at temperature 4 ^oC (kg/m³)

It is common to use the density of water at 4 ^oC (39^oF) as a reference since water at this point has its highest density of 1000 kg/m³ or 62.4 lb/ft³.

Specific Gravity - SG -  is dimensionless and has the same value in the SI system and the imperial English system (BG). Water is normally also used as reference when calculating the specific gravity for solids.

• Thermal Properties of Water - Density, Freezing temperature, Boiling temperature, Latent heat of melting, Latent heat of evaporation, Critical temperature ...

 

Specific Gravities for some common Materials

Substance	Specific Gravity - SG -
Acetylene	0.0017
Air, dry	0.0013
Alcohol	0.82
Aluminum	2.72
Brass	8.48
Cadmium	8.57
Chromium	7.03
Copper	8.79
Carbon dioxide	0.00198
Carbon monoxide	0.00126
Cast iron	7.20
Hydrogen	0.00009
Lead	11.35
Mercury	13.59
Nickel	8.73
Nitrogen	0.00125
Nylon	1.12
Oxygen	0.00143
Paraffin	0.80
Petrol	0.72
PVC	1.36
Rubber	0.96
Steel	7.82
Tin	7.28
Zinc	7.12
Water (4oC)	1.00
Water, sea	1.02

 

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