Density vs Relative Density: Difference and Comparison

Density and relative density are two concepts that help determine the volume and mass of a substance. Although the two may seem similar concepts, they are different.

The symbol, SI unit, measurement, and other names of density and relative density vary from each other.

Key Takeaways

  1. Density measures how much mass is contained in a given volume of a substance. In contrast, Relative Density is the ratio of the density of a substance to the density of a reference substance.
  2. Density is measured in units such as grams per cubic centimeter or kilograms per liter, whereas Relative Density is a dimensionless quantity.
  3. Density is an important physical property used to characterize materials, whereas Relative Density is mainly used in scientific and engineering applications.

Density vs Relative Density

Density is the measurement of mass per unit volume of a material substance, and there is density of solids, liquids and gases. It is represented by ρ, a lowercase Greek letter. Relative density is the measurement of the mass per unit volume of a material based on the given reference material.

Density vs Relative Density

The density of certain common solids, liquids, and gases is a part of every science textbook. The symbol of density is ρ, which is the lowercase Greek letter rho. Density depends on the volume of a body.

In addition, an increase in pressure causes a decrease in the density of an object by increasing its volume. The formula for mass is M=Vd, and the formula for volume is V=M/d.

Density provides a convenient way to measure the mass and volume of a substance.

The relative density of a substance indicates if the material will float or sink. If the relative density of a material is less than 1, it is less dense than the reference material.

However, if it is more than 1, then the substance is denser than the reference material. The factors that influence relative density are temperature, pressure, and the nature of the material.

Comparison Table

Parameters of ComparisonDensityRelative Density
SymbolThe symbol of density is ρ. The symbol of relative density is SG. 
Another NameAnother name of density is specific weight. Another name of relative density is specific gravity.
MeaningDensity measures the mass per unit volume. Density provides a convenient way to measure the mass and volume of a substance. Relative density measures the mass per unit volume in accordance with a given reference material. 
SI unitThe SI unit of relative density is kg/m3.Relative density has no SI unit. 
MeasurementDensity is specific to each substance. Different materials have varying densities. The densest known elements at room temperature are osmium and iridium.Relative density of a substance varies in accordance with the given reference material. 

What is Density?

Density refers to mass per unit volume. The formula for the same is d=M/V, where M is the mass, and V is the volume. At most times, density is expressed in grams per cubic centimetre or kilograms per cubic centimetre.

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Consider, for example, the density of Earth, which is 5.51 grams per cubic centimetre. Another example is the density of air, which is 1.2 kilograms per cubic meter. 

Density provides a convenient way to measure the mass and volume of a substance. The formula for mass is M=Vd, and the formula for volume is V=M/d.

The density of certain common solids, liquids, and gases is a part of every science textbook. The symbol of density is ρ, which is the lowercase Greek letter rho. 

The density and mass concentration of a pure substance are the same. However, different materials have varying densities. The densest known elements at room temperature are osmium and iridium.

The density of substances varies following pressure and temperature. This variation is the most prominent for gases, followed by liquids and solids.

Density depends on the volume of a body. In addition, an increase in pressure causes a decrease in the density of an object by increasing its volume.

However, there are some exceptions. In conclusion, the density of any substance is determined by its temperature, electric field, physical state, composition, allotropic shape, etc. 

density

What is Relative Density?

Relative density refers to the mass per unit volume of a substance concerning a specific given material. Another name for relative density is specific density.

At most times, the relative density of liquids calculates concerning water as the reference material. In contrast, the reference material taken into account for gases is air.

If the relative density is less than 1, it is less dense than the reference material. However, if it is more than 1, then the substance is denser than the reference material.

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If the relative density is equal to 1, then the material and the reference material have equal densities. Relative density has no SI unit. 

The symbol denoting relative density is SG. The relative density of a substance indicates if the material will float or sink. The relative density of rubbing oil is 0.79 grams/cm3, and the density of water is 1 gram/cm3.

Relative density is a physical quantity with no specific dimensions. Different substances have different relative densities. 

The factors that influence relative density are temperature, pressure, and the nature of the substance.

Different ways to calculate relative density are hydrometer, Pycnometer method, oscillating densitometer, buoyancy method, immersed body method, and hydrostatic method.

In conclusion, relative density measures the density of a given material. 

Main Differences Between Density and Relative Density

  1. Another name for density is specific weight. On the other hand, another name for relative density is specific gravity.
  2. The symbol of density is ρ. In contrast, the symbol of relative density is SG. 
  3. The SI unit of relative density is kg/m3. However, relative density has no SI unit.
  4. Density measures the mass per unit volume. In contrast, relative density measures the mass per unit volume following a given reference material. 
  5. Density is specific to each substance. On the other hand, the relative density of a substance varies in accordance with the given reference material. 
Difference Between Density and Relative Density
References
  1. https://ascelibrary.org/doi/abs/10.1061/JSFEAQ.0001642 
  2. https://ascelibrary.org/doi/abs/10.1061/AJGEB6.0000521 

Last Updated : 14 October, 2023

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19 thoughts on “Density vs Relative Density: Difference and Comparison”

  1. I’ve always struggled to understand the concept of relative density but this article has made it much clearer.

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