Specific Gravity Calculator — SG = ρ / ρ_ref
Specific gravity is the ratio of a substance's density to a reference density (usually water). Enter a known density or weigh your object in liquid (Archimedes method) to get the SG, density and whether the material floats.
Input method
kg/m³
kg/m³
Less dense than water — floats
- 1
Substance density
800 kg/m³ - 2
SG = ρ ÷ ρ_ref
800 ÷ 1,000 = 0.8000
How does this calculator work?
Specific gravity SG = ρ / ρ_ref (dimensionless). Using known densities: SG = substance_density / 1000. Using Archimedes weighing: SG = m_air / (m_air − m_liquid) × (ρ_liquid / 1000). SG < 1 floats, SG > 1 sinks. For a material with ρ = 800 kg/m³, SG = 0.8.
Formula
How this is calculated
Specific gravity (SG) is a dimensionless ratio that compares a material's density to a reference, almost always water at its maximum density (4 °C, ρ = 1000 kg/m³). SG < 1 means the material is less dense than water and floats; SG > 1 means it sinks. Because it is a ratio, SG is independent of unit system, which makes it useful for quick comparisons across materials tables.
If you already know the density, SG = ρ_substance / ρ_reference is immediate. The Archimedes method lets you measure SG without a calibrated densitometer: weigh the object in air (m_air), then weigh it while fully submerged in a liquid of known density (apparent mass m_liquid). The buoyant force equals the weight of displaced liquid, so m_air − m_liquid = ρ_liquid × V, giving the volume and hence the density. SG relative to water follows from multiplying by ρ_liquid/ρ_water.
Practical note: the Archimedes method assumes the object does not absorb or react with the liquid and is fully submerged with no air bubbles attached. Temperature affects water density (ρ_water = 999.7 kg/m³ at 20 °C vs 1000.0 at 4 °C); for precision work, use the actual liquid density at your measurement temperature.
Frequently asked questions
SG is widely used in brewing (wort concentration and alcohol potential), gemology (identifying minerals), petroleum refining (API gravity), soil mechanics, food science (sugar content via Brix), and quality control for coatings and chemicals. It is a fast, instrument-free way to characterise a substance.
Use a scale and a container of liquid. Hang the object from the scale with a thin thread so it is fully submerged without touching the container walls or base. Read the apparent mass. The difference between the air weight and submerged weight is the buoyant force, from which SG is calculated.
By convention the reference is water at 4 °C (39.2 °F) where ρ = 1000 kg/m³ exactly. Some industries (petroleum, beer) use 15 °C (59 °F) where ρ ≈ 999.1 kg/m³, introducing a small difference; always check which reference your data uses.
Also known as
TG we-Calculate Editorial Team. (2026). Specific Gravity Calculator — SG = ρ / ρ_ref [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/specific-gravity-calculator
TG we-Calculate Editorial Team. "Specific Gravity Calculator — SG = ρ / ρ_ref." TG we-Calculate. 2026. https://we-calculate.com/calculator/specific-gravity-calculator.
TG we-Calculate Editorial Team, "Specific Gravity Calculator — SG = ρ / ρ_ref," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/specific-gravity-calculator
@misc{wecalculate_specific_gravity_calculator, title = {Specific Gravity Calculator — SG = ρ / ρ_ref}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/specific-gravity-calculator}}, year = {2026}, note = {TG we-Calculate} }
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