What is Density? Definition, Units and Formulas

Density has a very important place in our daily life. Because due to density we can determine many things.

For example, whether a substance will float in water or not can be determined on the basis of density.

Apart from this, how much cargo a ship can carry can also be determined on the basis of density.

The measurement of density is very useful when determining how much force is required to move a liquid through a pipe.

So let us know what is called density, definition of density and what is its formula and what is the unit of density. 

What is Density?

Density is defined as its mass per unit volume. The ratio of the mass of an element to its volume is called density. That is, the mass of a unit volume of a substance is called density.

Density is denoted by the green letter ρ (rho). The unit of density in the international system is kg/m3

Water is considered a universal matter, and the density of water at 25 °C is 1000 kg/m 3 or 1 g/cm3.

You must have seen that if cotton is filled in a box and if stone is filled in the same box, then the box full of stone weighs more.

This is due to the density of the stone, as the density of the stone is more than the density of cotton.

That is, we can say that the density of lighter substances is less and the density of heavy substances is more.

Density is an important property of substances, and does not depend on the amount of mass of the substance, as it is the mass/volume ratio that remains constant for the same substance. This property makes it possible to separate one substance from another.

The density of all the substances found on Earth varies. Some substances have very low density and some substances have very high density.

Just as the density of gases is very low, the density of solids like iron is very high. 

That's why there are many units to measure density. Such as kg/m3 , g/cm3   etc.

So far we know what is density. That is, now we have become familiar with the definition of density, so let us now know what is the formula of density and its unit.

What is the formula for density?

According to the definition of density, we can represent the formula for density as follows-


 Where ρ = density, m = mass and V = volume.

What is the unit of density?

Density is a vector sum. The SI unit of density is kilograms per cubic meter (kg/m3 ). while in the CGS method the unit of density is (g/cm3).

Density is same in most of the conditions but some change in density is observed as the temperature increases or decreases.

change in density

Changing the pressure or temperature of an object will generally change its density. As the temperature decreases, the movement of molecules in a substance slows down; As they slow down, they require less space, which increases the density.

Conversely, an increase in temperature usually leads to a decrease in density. But there are exceptions: for example, water expands slightly when it freezes, so ice is less dense than liquid water. Ice floats on water because the density of ice is low.

After getting information about what is density and the unit and formula of density, now we will get information about the type of density and its examples.

Types of Density- 

Absolute density 

The density which we have mentioned above is the same density as absolute density. That is, absolute density is the ratio between mass and volume.

Relative density

The relative density of a substance is defined as the ratio of its density to that of water at 4° C .

In other words, we can say that the relative density is the density which is the density of a substance which is represented relative to the density of another substance.

Formula for relative density-

The formula for relative density is as follows:

Relative Density = Physical Density / Density of Water

It is necessary to note here that

Both the density of the material and the water must be measured under the same pressure and temperature conditions, and expressed in the same units.

Apparent density

Apparent density is calculated from the ratio between the mass of a substance and its volume, which also includes pores and spaces with air:

The formula for apparent density-

Apparent density = mass / volume = (particle mass + air mass) / (particle volume + air volume)

examples of density

  • The density of blood is 1060 kg/m 3  .
  • The lightest metal is lithium, which has a density of 530 kg/ m3  .
  • The density of quark plasma is 1 × 10 19 kg / m 3 .
  •  Osmium is the densest metal known with a density of 22,570 kg/m 3 .

Related Articales


Download Our App (1Mb Only)
To get FREE PDF & Materials