Surface Area Lesson for Kids

Instructor: Bethany Calderwood

Bethany has taught special education in grades PK-5 and has a master's degree in special education.

This lesson explains surface area. You will learn how to use length and width to calculate the areas of the surfaces of an object and add them all together to find the total surface area.

What Is Surface Area?

Lucas has a pile of empty cereal boxes. He wants to cover them with red paper and make them into building blocks. How much paper does Lucas need to cover one box?

To find out how much paper is needed, Lucas has to find the surface area of the cereal box. Surface area is a measurement of all the space that the surface of a three dimensional shape (a shape with height, width and depth) takes up. In other words, surface area is the total of all the areas of each of the sides of an object.

A cereal box is a three-dimensional object.
cereal box

Examining the Sides

How many sides are on one cereal box? There is a top and bottom--those are the same size. Then there is a front and back--those are the same size. And finally there are the two narrow sides--those are the same size. Look at the diagram that shows what the cereal box would look like if it were cut open and flattened out:

If you unfold a cereal box, you get a clear picture of all of its sides.
cereal box with measurements

To find the surface area of the cereal box, Lucas will have to find the areas of all six sides.

Finding Areas of the Sides

Look again at the diagram. Each side of the cereal box is a rectangle. The formula Lucas needs to find the area of a rectangle is:

  • area = length x width

So, let's find the area of each side.

Area of the Top and Bottom

The length of the top is 7 inches, and the width is 2 inches.

7 inches x 2 inches = 14 square inches.

The area of the top is 14 square inches.

The top and bottom are the same, so the area of the bottom is also 14 square inches.

Area of the Front and Back

The length of the front is 12 inches, and the width is 7 inches.

12 inches x 7 inches = 84 square inches.

The area of the front is 84 square inches.

The front and back are the same, so the area of the back is also 84 square inches.

Area of the Two Narrow Sides

The length of one narrow side is 12 inches, and the width is 2 inches.

12 inches x 2 inches = 24 square inches.

The area of one narrow side is 24 square inches.

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