Share:
How It Works
Specific gravity (SG) is the dimensionless ratio of a substance's density (or specific weight) to that of a reference — usually water at 4 °C (1,000 kg/m³). An SG less than 1 means the substance floats in water; greater than 1 means it sinks. You can calculate SG from either density ratios or specific weight ratios.
Example Problem
Olive oil has a density of 920 kg/m³. What is its specific gravity relative to water?
- SG = 920 / 1,000 = 0.92
Since SG < 1, olive oil floats on water.
Frequently Asked Questions
What is specific gravity used for?
Specific gravity is widely used in geology (mineral identification), brewing (measuring sugar content), petroleum (API gravity), and quality control to verify material purity.
Is specific gravity the same as density?
No. Density has units (kg/m³), while specific gravity is a dimensionless ratio. Numerically, specific gravity relative to water at 4 °C equals the density in g/cm³.
Can specific gravity change with temperature?
Yes. Both the substance and reference densities change with temperature, so specific gravity measurements should state the temperature conditions (e.g., SG at 20 °C/4 °C).
Related Calculators
- Density Calculator — calculate density from mass and volume.
- Specific Volume Calculator — find volume per unit mass.
- Fluid Pressure Calculator — determine pressure in a fluid column.
- Stokes Law Calculator — calculate settling velocity using particle and fluid densities.
- Density Converter — convert density units between kg/m3, lb/ft3, and g/cm3.
Reference: Lindeburg, Michael R. 1992. Engineer In Training Reference Manual. Professional Publication, Inc. 8th Edition.