By Zencalcy Editorial TeamLast reviewed About us
Specific gravity (SG) is the ratio of the density of a substance to the density of a reference substance, usually water at 4 °C (ρ₍w₎ ≈ 1000 kg/m³). It is a dimensionless quantity.
Ratio of a material's density to the density of water.
SG = ρ / ρ₍w₎
SG is dimensionless. A value above 1 indicates the material sinks in water; below 1 it floats.
| Symbol | Meaning |
|---|---|
| SG | Specific gravity (relative density). |
| ρ | Density of the material. |
| ρ₍w₎ | Density of the reference substance (water). |
SG = ρ / ρ_water = 2700 / 1000 = 2.7, typical of aluminium.
Continue with the Engineering Stress‑Strain Calculator, True Stress Calculator, or the True Strain Calculator — or browse more materials and elasticity tools and all physics calculators.
No. Specific gravity is a ratio; density has units of mass per volume.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Content updated: September 2026