Density Worked Example Problem

Calculating Density of a Substance

Density is mass per unit volume of a solid, liquid, or gas.
Density is mass per unit volume of a solid, liquid, or gas. Dave King / Getty Images

Density is a measure of how much matter is in a space. This is a worked example of how to calculate the density when given the volume and mass of a substance.

Sample Density Problem

A brick of salt measuring 10.0 cm x 10.0 cm x 2.0 cm weighs 433 grams. What is its density?

Solution:

Density is the amount of mass per unit volume, or:
D = M/V
Density = Mass/Volume

Step 1: Calculate Volume

In this example, you are given the dimensions of the object, so you have to calculate the volume.

The formula for volume depends on the shape of the object, but it's a simple calculation for a box:

Volume = length x width x thickness
Volume = 10.0 cm x 10.0 cm x 2.0 cm
Volume = 200.0 cm3

Step 2: Determine Density

Now you have the mass and the volume, which is all the information you need to calculate density.

Density = Mass/Volume
Density = 433 g/200.0 cm3
Density = 2.165 g/cm3

Answer:

The density of the salt brick is 2.165 g/cm3.

A Note About Significant Figures

In this example, the length and mass measurements all had 3 significant figures. So, the answer for density should also be reported using this number of significant figures. You'll have to decide whether to truncate the value to read 2.16 or whether to round it up to 2.17.