Relative density


Bodies have a number of important characteristics that allow you to study them and observe the way they behave. One of them is the relative density, whose main function is to be able to carry out a series of measurements on the degree of concentration of the mass that a given volume has.


What is relative density?

The relative density, also known as the volumetric density or mass density of a certain body, is the quotient that exists between the mass and the volume of the body.

  • Definition of relative density
  • How Relative Density Is Calculated
  • Relationship with temperature
  • What is it for
  • How it differs from absolute density
  • Importance
  • Examples

Definition of relative density

To have a good understanding of relative density it is necessary to remember that bodies and matter have density which is the amount of mass of volume , this is also an invariable value. Relative density is known as the relationship between the density of a certain substance and the density of a reference substance , which in most cases is water . So, for example, when we refer to a substance that has an amount of density of 5, it actually means that it has a density five times that of water, when it comes to solid or liquid materials.


How Relative Density Is Calculated

In order to calculate the relative density mathematically, the following formula is used :

Pr = p / p0

where pr means relative density , p is used to show the density of the substance and p0 represents the density of the substance that has been taken as a reference . It is important to mention that density must be expressed in kilograms per cubic meter as follows: kg / m 3 although it is also common to express it in g / cm 3 .

Relationship with temperature

Temperature and relative density are closely linked because when there is an increase in the same in a matter, there is an increase in the fixed volume of the body, otherwise, when the temperature is decreased then a reduction in the volume. At the same time and for the same reason, the relative density can vary depending on the state in which it is found, being higher in solid states of matter, lower in liquids and even lower in those that are in the gaseous state.

What is it for

There are several uses for relative density. It is an effective means by means of which the level of buoyancy that a substance has in a certain fluid can be measured and quantified and it is also used to determine the density of an unknown substance from the density of another of which already information is available. It is a formula widely used in the field of science , mainly by mineralogists and geologists who use it to properly determine the minerals found within rocks or other types of samples. The people who are in charge of determining and identifying gemstones they also use science. In the field of industry it is necessary to, through it, be able to establish the different concentrations that exist in aqueous solutions.

How it differs from absolute density

The main difference is that the absolute density of a body is the quotient that exists between the mass of a body or substance and the volume it occupies. The volume always depends on the temperature , the pressure and the density at the same time it will depend on these two aspects. The absolute density then has aspect dimensions that are not found in the relative density.


The relative density turns out to be of great importance for several of the activities that are carried out daily and to evaluate the conditions of the materials that influence in one way or another in daily life. It is a property that can, for example, measure the index with the soil mainly in gravels and sands, which are needed for construction. It is vital to be able to measure the indexes or degrees of compaction in the land , which is why it is a key aspect within the field of geotechnics .

Its importance also lies in the mixture of substances and in their configuration, being able to know the relative density of a given fluid will allow us to understand the way in which it can influence others and determine at the same time the power that is needed. to be able to make different types of mixes correctly.


  • Relative density of water: 1 g / cm³
  • Relative density of oil: 5 g / cm³
  • Relative density of urine: 1.016 – 1.022 g / cm³
  • Relative density of mercury : 6 g / cm³
  • Relative density of propane : 2 g / cm³
  • Relative density of gasoline : 68 g / cm³
  • Relative density of ice: 92 g / cm³
  • Relative density of aluminum: 7 g / cm³
  • Relative density of alcohol: 79 – 0.80 g / cm

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