Specific Gravity Calculator
Specific gravity (SG) is the ratio of a substance's density to the density of a reference substance, usually water at 4°C (1000 kg/m³ or 1 g/cm³). It is a dimensionless number. If SG is less than 1, the substance floats in water. If greater than 1, it sinks. Specific gravity is widely used in brewing, geology, materials science, and fluid engineering.
Here's the formula:
SG = Density of substance / Density of reference
Since the reference for liquids and solids is almost always water at 4°C (its maximum density), specific gravity numerically equals the density in g/cm³. For gases, the reference is usually air at standard conditions.
Common specific gravities:
- Ice: 0.917 (floats in water)
- Gasoline: 0.72-0.78 (floats)
- Seawater: 1.025 (denser than fresh water)
- Aluminum: 2.7
- Iron: 7.87
- Gold: 19.3
- Mercury: 13.6 (iron floats on mercury)
In brewing, specific gravity readings track fermentation progress. Wort starts around SG 1.050 and finishes near 1.010 as yeast converts sugar to alcohol. In geology, specific gravity helps identify minerals. In medicine, urine specific gravity (1.002 to 1.035) indicates hydration status.