Specific gravity

Specific Gravity (SG) is a special case of relative density.

It is defined as the ratio of the density of a given substance, to the density of water (H₂O). Substances with a specific gravity greater than 1 are heavier than water, and those with a specific gravity of less than 1 are lighter than water.

[math]\displaystyle{ \mbox{SG} = \frac{\rho_\mathrm{substance}}{\rho_\mathrm{H2O} } }[/math] ^[1]

SG is by definition dimensionless and therefore not dependent on the system of units used (e.g. slugsft⁻³ or kgm⁻³), assuming that the units are consistent. Based on the SG-value of a given substance, the density of that substance can be calculated.

Specific Gravity Media

A United States Navy Aviation boatswain's mate tests the specific gravity of JP-5 fuel
An empty glass pycnometer and stopper
A full pycnometer, photographed on 5 mm squares.

Related pages

Other websites

Specific Gravity Calculator Archived 2022-09-14 at the Wayback Machine

References

↑ The density of the denominator, or reference, is [math]\displaystyle{ \rho_\mathrm{H2O} }[/math] = 1000kgm^-3 (at 4°C/39.2°F) in SI units.

Fundamentals of Fluid Mechanics Wiley, B.R. Munson, D.F. Young & T.H. Okishi
Introduction to Fluid Mechanics Fourth Edition, Wiley, SI Version, R.W. Fox & A.T. McDonald
Thermodynamics: An Engineering Approach Second Edition, McGraw-Hill, International Edition, Y.A. Cengel & M.A. Boles

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[1] The density of the denominator, or reference, is [math]\displaystyle{ \rho_\mathrm{H2O} }[/math] = 1000kgm^-3 (at 4°C/39.2°F) in SI units.

[1]