How to Calculate Specific Gravity

Specific Gravity is the ratio of the density of a soil to the density of water.

$latex SG = \frac{\rho_s}{\rho_w}&s=2$
SG = Specific Gravity (dimensionless)
ρs = bulk density of soil (kg/m3 or lb/ft3)
ρw = bulk density of water (kg/m3 or lb/ft3)
= 1000 kg/m3 (62.4 lb/ft3)

Specific Gravity of Various Substances

Substance Specific Gravity
Water 1.0
Organic Soils 2.5
Most soils 2.65 – 2.70
Clay 2.9
Iron 7.9
Copper 9.0
Gold 19.3

Relative Density

Relative Density is related to Specific Gravity in that it compares the density of a substance to a certain reference density rather than that of water.

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