Specific Gravity Calculator

What is Specific Gravity?

Specific gravity (SG) is the ratio of a substance's density to the density of a reference substance — typically water (1,000 kg/m³ at 4°C) for liquids and solids, or air for gases. Being dimensionless, it allows easy comparison of densities across unit systems.

The Formula

SG = ρ_substance / ρ_reference

For liquids vs water: SG = ρ_liquid / 1000 (when density is in kg/m³) For gases vs air: SG = M_gas / M_air = M_gas / 28.97 (using molar masses)

Common Specific Gravities

| Substance | SG | |-----------|-----| | Fresh water | 1.000 | | Sea water | 1.025 | | Gasoline | 0.72 | | Diesel | 0.85 | | Crude oil | 0.79–0.88 | | Mercury | 13.6 | | Concrete | 2.3 | | Steel | 7.8 | | Aluminium | 2.7 |

How to Use This Calculator

Enter density in kg/m³ to get specific gravity, or enter SG to get density. Also converts to API gravity (petroleum industry standard) and Baumé scale.

Practical Examples

Example 1: Battery acid (sulfuric acid solution, density 1,250 kg/m³). SG = 1.25. A hydrometer reading of 1.25 indicates a fully charged lead-acid battery.

Example 2: Natural gas (mostly methane, M=16). SG vs air = 16/28.97 = 0.552 — lighter than air, hence it rises when leaked.

Applications

Specific gravity is used in: hydrometers (battery, alcohol, coolant testing), API crude oil classification, concrete mix design, and liquid density measurement for process control.