Density explained!

Density of materials explained

what is density

What is density?

Each material has a different density, the difference depends on how the materials particles are packed together. If the particles of a material are stored very neatly, and closer together, then more particles will be able to fit into the volume. Since particles have mass, the more particles you can fit into the volume, the more the material will weigh.

Density is just a measurement of how much mass is in a given volume. We measure density in the SI units of kg/m3 (kilograms per cubic meter) usually density is listed as the Greek symbol Rho ρ.

Good news! we have already listed the typical density of common metals, just click here to view the table. (opens in a new tab).

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Why do we need to know the density of materials

Knowing the density of materials is very useful. Designers will estimate the weight of a product by multiplying the volume by the density of a material, this is very useful if a product had to be designed within a certain weight limit. You can also identify a material by measuring its volume and mass.

How to calculate density

Density is calculated simply by dividing the mass (m) of an object by its volume (V).

ρ = m / V

Mass has the SI units of kilogram (kg) and volume has the SI units of cubic meter (m3)

ρ = kg / m3


You have a large solid metal block but are unsure if it is made from Aluminium or Stainless steel. You measure it and find it has a volume of 2m3 and a total mass of 5400kg.

You calculate it’s density using the formula

ρ = m / V

ρ = Density = kg/m3

m = Mass = kg

V = Volume = m3

So drop the numbers of your measurements into the equation:

ρ = 5400kg ÷ 2m3

and the answer is

ρ = 2700kg/m3

Aluminium has a density of approx 2705kg/m3 and Stainless Steel has a density of approx 7982kg/m3. So the block must be made from Aluminium. Click here to find the density of other common metals.

Important – Density of fluids

The density of solids remains almost constant, however, the density of a fluid will vary depending on pressure and temperature.

If a fluid is heated, then its mass will remain constant but the volume will increase, this means that the density will decrease.

If a fluid is compressed, the mass remains the same but the volume decreases so the density will increase.


  1. I think is like a measure of mass per unit volume. Density is a measure of mass per volume. An object made from a relatively dense material (such as iron) will have less volume than an object of equal mass from a less dense substance (such as water).

  2. what i learned is that the measure of the mass of an object per unit volume how a pese of wood can float but a small rock sinks that is because of how it is shaped


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