Specific Gravity Calculator
Find a substance's specific gravity from density.
Water = 1000 kg/m³
Results update as you type.
How it works
Specific gravity, also called relative density, compares a substance's density to that of a reference material, and this calculator computes it. You enter the density of your substance and, optionally, the reference density, which defaults to water at 1000 kilograms per cubic meter, and it returns the specific gravity. Because it divides one density by another of the same units, the result is a pure number with no units, which makes it convenient for comparing materials regardless of the measurement system. The most common reference is water, so a specific gravity of 0.8 means the substance is 80 percent as dense as water. The key practical meaning is buoyancy: a specific gravity greater than one means the material is denser than water and will sink, while less than one means it floats, which is why oil with a specific gravity around 0.9 floats on water. Specific gravity is widely used in chemistry, geology, brewing and winemaking, petroleum, gemology, and quality control to identify substances, check purity and concentration, and predict flotation. For gases, air is often used as the reference instead of water. This calculator lets you set any reference so you can compute relative density against whatever standard your field uses. Enter the substance density and reference density to compute specific gravity.
SG = substance density / reference density
Specific gravity, or relative density, divides a substance's density by the density of a reference, usually water at 1000 kilograms per cubic meter. Because it is a ratio of like units, it is dimensionless. A specific gravity above one means the substance is denser than the reference and will sink, while below one means it is less dense and will float.
Source:Physics (fluid properties)
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter substance density.
- 2
Adjust the options
Adjust reference density if they apply — sensible defaults are already set.
- 3
Read your result
Specific gravity updates instantly as you type — no button to press.
Frequently asked questions
What is specific gravity?
Specific gravity, or relative density, is the ratio of a substance's density to the density of a reference material, usually water. Because it compares like units, it is a dimensionless number. It tells you how dense a substance is relative to the reference and whether it will sink or float in it.
How do you calculate specific gravity?
Divide the substance's density by the reference density. With water as the reference at 1000 kilograms per cubic meter, a substance of 800 kilograms per cubic meter has a specific gravity of 0.8. The calculator does this and lets you change the reference density for gases or other standards.
What does a specific gravity above or below one mean?
A specific gravity greater than one means the substance is denser than the reference, so it sinks in it, while a value below one means it is less dense and floats. With water as the reference, oil at around 0.9 floats, and most metals, with values well above one, sink.
Why is specific gravity dimensionless?
Specific gravity divides one density by another, and since both are measured in the same units, those units cancel out, leaving a pure number. This makes specific gravity independent of the measurement system, so the same value results whether you work in metric or imperial units, which is a major convenience for comparing materials.
Where is specific gravity used?
It is used across many fields: in brewing and winemaking to track fermentation, in geology and gemology to identify minerals and gems, in petroleum to grade crude oil, in chemistry to check concentration and purity, and in engineering for buoyancy and flotation. It is a quick, reliable way to characterize and identify substances.