Volume & Capacity: Lesson for Kids

Instructor: Kelley Lipke

Kelley has been teaching middle school for six years and has a master's degree in educational administration.

Have you ever wondered why we measure our drinks in liters and gallons? What about how much water it takes to fill up a fish tank or a swimming pool? Both of these ideas are related to volume and capacity. Keep reading to find out more!

What is Volume?

Max received a new fish tank for his birthday. Before he can put his fish in it, he needs to figure out how much water he can use to fill the aquarium.

Volume is the amount of space inside a solid figure. These figures are 3-dimensional, meaning the figure has three parts including length, width, and height. We measure volume in cubic units.


What is Capacity?

Capacity is how much liquid a 3-dimensional figure can hold. We can measure capacity in multiple ways:

Metric System: liters and milliliters

Customary System: cups, pints, quarts, and gallons

In the metric system, we know that 1,000 milliliters equal 1 liter.

In the customary system, we are aware that:

2 cups = 1 pint

2 pints = 1 quart

4 quarts = 1 gallon


The capacity of a figure may change, while the volume stays the same. In this example, Max's tank will not change in size, but he can add or subtract the amount of water he puts in the tank.

Finding Volume

To find out how much water the tank can hold, Max needs to measure the tank's volume. The formula for the volume of a rectangular prism is volume = length times width times height. So, Max will measure each of these dimensions and then multiply them.


V = l x w x h

V = 14 in. x 5 in. x 10 in.

V = 70 in. x 10 in.

V = 700 cubic inches

How much water can the new tank hold? The volume or amount of water the tank can hold is 700 cubic inches.

Measuring Capacity

Let's say that the directions for the fish tank say to fill with 2 gallons of water. However, Max only has a 1-pint container for measuring. Max needs to figure out how many times he needs to fill the pint to equal 2 gallons.

We know that 1 gallon is made up of 4 quarts. But how many pints make 1 quart? 2 pints make 1 quart. Therefore, 2 x 4 = 8. Max needs to fill 8 pints to make 1 gallon of water.

Since Max needs 2 gallons of water to fill the tank, he will multiply 8 times 2, which gives him an answer of 16.

To fill the fish tank, Max needs to fill the pint container 16 times.

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