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.

The density of the denominator, or reference, is  = 1000kgm-3 (at 4°C/39.2°F) in SI units.

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.

Related pages
 Buoyancy
 Fluid mechanics
 Relative density

Other websites
 Specific Gravity Calculator 

References

 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

Category:Physics