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Engineering/Terminology

Specific Gravity (Relative Density)

by 유일민 2015. 8. 26.

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 = ρsubstance / ρH2O         (3)

where

SG = Specific Gravity of the substance

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

ρH2O = density of water - normally at temperature 4 oC (kg/m3)

It is common to use the density of water at oC (39oF) 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

SubstanceSpecific Gravity
SG -
Acetylene0.0017
Air, dry0.0013
Alcohol0.82
Aluminum2.72
Brass8.48
Cadmium8.57
Chromium7.03
Copper8.79
Carbon dioxide0.00198
Carbon monoxide0.00126
Cast iron7.20
Hydrogen0.00009
Lead11.35
Mercury13.59
Nickel8.73
Nitrogen0.00125
Nylon1.12
Oxygen0.00143
Paraffin0.80
Petrol0.72
PVC1.36
Rubber0.96
Steel7.82
Tin7.28
Zinc7.12
Water (4oC)1.00
Water, sea1.02


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