SpecificGravity
Compute specific gravity (relative density) of any substance. Enter density or pick from common materials for SG, buoyancy status, and comparison charts.
About This Calculator
The Specific Gravity Calculator (also known as the relative density calculator) computes the ratio of a substance's density to the density of water. Specific gravity tells you immediately whether a material will float or sink in water, and is widely used in brewing, automotive maintenance, gemology, petroleum engineering, and materials science.
The calculation uses the formula SG = ρ / ρ₀, where ρ is the density of the substance and ρ₀ is the density of water at 4°C (1000 kg/m³ or 62.428 lb/ft³). Since both densities are in the same units, specific gravity is a unitless number. For example, ice has a density of 917 kg/m³, giving SG = 0.917 — it floats. Steel at 7850 kg/m³ gives SG = 7.85 — it sinks.
How to Use
You can enter density directly in kg/m³, or select from over 40 common materials (aluminum, gold, wood, mercury, etc.) whose densities are built into the calculator. The result shows the specific gravity, buoyancy classification, and a comparison chart.
Regional Notes
Worldwide: The standard reference is water at 4°C (1000 kg/m³). US customary units (lb/ft³) are not used in the standard formula, but the density value can be entered in any unit as long as both values match.
Frequently Asked Questions
What is specific gravity?
Specific gravity (also called relative density) is the ratio of a substance's density to the density of water at 4°C (1000 kg/m³). It is a unitless number that indicates how dense a material is compared to water.
How do you calculate specific gravity?
Specific gravity is calculated by dividing the density of the substance by the density of water (1000 kg/m³ at 4°C). The formula is SG = ρ_substance / ρ_water.
What does a specific gravity less than 1 mean?
A specific gravity less than 1 means the substance is less dense than water and will float. Examples include ice (0.92), wood (0.6), and olive oil (0.92).
What does a specific gravity greater than 1 mean?
A specific gravity greater than 1 means the substance is denser than water and will sink. Examples include steel (7.85), mercury (13.57), and gold (19.3).
Is specific gravity the same as density?
No. Density is an absolute measure of mass per unit volume (kg/m³), while specific gravity is a relative ratio comparing a substance's density to water. Specific gravity has no units.
What is the specific gravity of water?
The specific gravity of water is exactly 1, since it is the reference substance. At 4°C water has its maximum density of 1000 kg/m³.
How is specific gravity used in industry?
Specific gravity is used in brewing to measure alcohol content, in automotive to check battery electrolyte density, in gemology to identify gemstones, in petroleum to grade crude oil (API gravity), and in quality control for liquids and solids.
Does temperature affect specific gravity?
Yes. Density changes with temperature for most substances, so specific gravity also changes. Standard specific gravity values are typically quoted at 4°C for water and 20°C for the substance.