Financial term · Reviewed August 17, 2026
Specific gravity
Specific gravity: A substance's density relative to water. Values above 1 sink in water; values below 1 float. The Density Calculator returns this figure from density = mass ÷ volume. At that calculator’s documented worked-example inputs the density (g/cm³) is 2; holding every other input steady, moving mass (g) from 80 to 120 moves it from 1.6 to 2.4, a spread of 0.8.
Density expressed as a plain ratio against water, with no units attached. That makes it directly comparable across measurement systems and immediately readable: above one sinks, below one floats. Brewers, mechanics and lab technicians all use it for exactly that reason. Brewers use it to track fermentation, because sugar dissolved in water raises density and yeast consuming that sugar lowers it again. The reading falls as the beer ferments. Mechanics use the same idea on battery electrolyte and coolant.
| Term | Specific gravity |
|---|---|
| Category | Science & Electronics |
| How it is found | Density = mass ÷ volume |
| Worked example | Density (g/cm³): 2 |
| Computed by | Density Calculator |
| Related terms | 2 defined in this glossary |
Before you rely on it
What to check
Check the reference temperature.
The common error
Where people go wrong with specific gravity
Comparing readings taken at different temperatures. Water's own density shifts, and precise work needs a stated reference.
Worked through
Specific gravity in plain numbers
Specific gravity is density compared with water, which is about 1,000 kilograms per cubic meter. Aluminum has a specific gravity near 2.70, so a liter of it weighs about 2.7 kilograms. Ice sits near 0.92 and floats with about 92% submerged. Seawater is about 1.025. Because the ratio is a pure number, it has no units. Measure a rock at 2.65 and you know a cubic foot of it weighs about 2.65 times a cubic foot of water, roughly 165 pounds; a hydrometer reading of a lead-acid battery's electrolyte, around 1.265 for a full charge, is a familiar specific gravity check.
Easily confused
Specific gravity and its neighbours
Specific gravity is not density itself, though they are closely related. Density carries units, such as kilograms per liter. Specific gravity is the ratio to the density of a reference, almost always water at a set temperature, so it is dimensionless. Relative density is the modern name for the same thing, and it is also different from weight and from viscosity. For gases the reference is usually air. Buoyancy depends on the ratio of an object's density to that of the fluid, so specific gravity above 1 sinks in water and below 1 floats.
In real decisions
Where specific gravity turns up
Brewers, winemakers and battery technicians use hydrometers to read it. Geologists use it to identify minerals. Engineers use it for fuels, oils, soils and aggregates. Jewelers use it to test gemstones. Doctors and labs check urine specific gravity as a hydration indicator; a calculator converts between density and specific gravity for a given reference temperature.
Know the edges
Where specific gravity stops being reliable
Temperature changes density, so readings must be at the calibration temperature or corrected. The reference must be stated. Porous materials complicate measurement. This page is educational. For laboratory, medical or safety uses, follow proper procedures and official standards.
Quick answers
What people ask about specific gravity
What is the specific gravity of water? One, by definition, at the reference temperature. Materials above 1 sink, and below 1 float.
How do I measure it at home? Use a hydrometer for liquids, or compare the weight of a sample in air and in water for solids. Note the temperature.
Why do brewers measure it? Sugar dissolved in a liquid raises its density. Readings before and after fermentation show how much sugar was converted.
How is it used to check antifreeze or battery acid? A hydrometer floats higher in denser liquids. The reading shows concentration or state of charge. Follow safety rules when handling chemicals.
What is API gravity? A scale used for petroleum that is related to specific gravity. Higher API means lighter oil. The two convert by formula.
Does specific gravity depend on temperature? Yes. Density changes with temperature, so readings are corrected or taken at a reference temperature. Note it whenever you record a result.
Put it to work
How specific gravity is calculated
At the density calculator’s worked-example inputs, density (g/cm³) is 2, specific gravity (relative to water) is 2. Moving mass (g) from 80 to 120 moves that first figure from 1.6 to 2.4.
These are exact physics and chemistry formulas. Real-world results add tolerances from component quality, temperature and measurement error that this calculator does not model.
Keep reading
Nearby in the glossary
- ← Sortino ratio
- Standard deduction →
- All 174 defined termsThe complete Free Calculators Online financial glossary.