Specific Gravity Formula

Specific Gravity Formula

Specific Gravity, or relative gravity, is a dimensionless quantity defined as the ratio of a substance’s density to the density of water at a certain temperature.

Specific Gravity

Specific gravity is defined as the ratio of an object’s density to that of a reference material. Furthermore, the specific gravity of an object can indicate whether it will sink or float in reference material. Furthermore, the reference material is water, which has a density of one gramme per cubic centimetre or one gramme per millimetre.

In layman’s terms, specific gravity determines whether an object sinks or floats in water. Furthermore, many factors influence whether an object will float or sink.

Specific Gravity
Dry Air 0.0013
Alcohol 0.82
Carbon dioxide 0.00126
Cast Iron 7.20
Petrol 0.72
Rubber 0.96
Wood Oak 0.77
Nylon 1.12


The object’s density describes how heavy or compact the object is in the given volume. We also calculate it in mass per unit volume. It is also expressed as grammes per cubic centimetre (g/cm3), grammes per millimetre (g/mL), or kilogrammes per litre (kg/L).

Density is defined as the heaviness or lightness of an object in a given volume. Furthermore, because density is directly proportional to mass, the object with the most molecules will have a higher density, while the object with the fewest molecules will have a lower density.

Physics is a natural science that studies matter, its fundamental constituents, motion and behaviour in space and time, as well as the related entities of energy and force. Physics is one of the most fundamental scientific disciplines, with the primary goal of understanding how the universe functions. A physicist is a scientist who specialises in the field of Physics.

Specific Gravity Formula

The Specific Gravity Formula uses water as its reference substance, and the formula is the ratio of an object’s density to the density of water. The Greek Symbol Rho also indicates density.

The formula is as given below:

Specific Gravity = Density of Water at 4°C / Density of the given substance

Specific Gravity =  ​= ​ρsubstance​​​ / ρH2​O


ρsubstance ​= Density of the given substance

ρH2​O​ = Density of Water at 4°C​

The specific gravity has no unit of measurement because the numerator and denominator of the formula are the same and cancel each other out.

Solved Example on Specific Gravity Formula

A hydrogen gas has a mass of 50 gm and the volume of the water (reference material) is 5 mL. Calculate the specific gravity of the substance?

Solution: Given that,

m = 50 g

V = 5 mL

ρ = 1 g/mL

Then the density of the substance is,

ρ’ = 50 g/5 mL = 10 g/mL


Specific Gravity = ρsubstance/ρH2O = 1 g/mL / 10 g/mL = 0.1

Hence, the density of the substance is 10 g/mL and the specific gravity is 0.1.


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FAQs (Frequently Asked Questions)

1. What is specific gravity?

The ratio of a material’s density to the density of another substance (such as pure water) used as a reference when weighing in air.

2. What is the SI unit of specific gravity?

It has no unit.

3. Is specific gravity same as density?

Density has units, but Specific Gravity is dimensionless.