Specific Gravity Calculator
Calculate specific gravity, relative density, and compare material density to water.
SG = ρ_material / ρ_water (1000 kg/m³)
What Is the Specific Gravity Calculator?
The Specific Gravity Calculator computes the specific gravity (relative density) of a substance by comparing its density to the density of a reference material — typically water at 4°C (1000 kg/m³). A specific gravity greater than 1 means the substance is denser than water and will sink; less than 1 means it will float.
Formula
How to Use
Enter the density of the substance in kg/m³, g/cm³, or lb/ft³. The calculator divides by the reference density (water at 1 g/cm³) to give specific gravity. Alternatively, enter the weight of the object in air and submerged in water to calculate SG using Archimedes' principle.
Example Calculation
Gold density = 19,300 kg/m³. SG = 19,300 ÷ 1000 = 19.3. Ethanol density = 789 kg/m³. SG = 789 ÷ 1000 = 0.789 (floats on water). Object weighs 50 N in air and 30 N submerged: SG = 50 ÷ (50−30) = 50/20 = 2.5.
Understanding Specific Gravity
Specific gravity is a dimensionless measure of a substance's density relative to a reference substance — almost always water at its maximum density (4°C, 1000 kg/m³). Because it is a ratio, specific gravity has no units and is easy to compare across materials and measurement systems.
In industrial applications, specific gravity is measured with a hydrometer — a weighted float that sinks deeper in less-dense liquids. Brewers use it to track fermentation progress (wort gravity decreases as sugars convert to alcohol). Petroleum engineers use API gravity (a transformed specific gravity scale) to classify crude oil types.
Specific gravity also appears in geology and mining, where it helps identify minerals: quartz has SG ≈ 2.65, feldspar ≈ 2.55, and pyrite ≈ 5.0. In construction, knowing the specific gravity of aggregates is essential for concrete mix design. This calculator handles any density unit and instantly converts to the dimensionless SG value.
Frequently Asked Questions
What is specific gravity used for?
Specific gravity is used in geology (mineral identification), brewing (measuring alcohol content), petroleum refining (API gravity), quality control, and flotation process design. It is a dimensionless number easy to compare across materials.
What is the specific gravity of water?
By definition, water at 4°C has a specific gravity of exactly 1.000. Other temperatures give slightly different densities, so SG changes marginally with temperature.
How does specific gravity relate to buoyancy?
Objects with SG < 1 float in water; those with SG > 1 sink. The buoyant force equals the weight of displaced water, which equals the object's volume times water density times g.
What are some common specific gravity values?
Ice: 0.92, Wood (oak): 0.75, Aluminum: 2.7, Iron: 7.87, Lead: 11.3, Gold: 19.3, Mercury: 13.6. Petroleum products range from 0.7 to 0.9.
Is this calculator free?
Yes, completely free with no account required.