Find out all kinds of interesting facts about the five-sided shape called the pentagon! Learn about this shape, the different types of pentagons, examples of pentagons and why it’s called a pentagon.

What Is a Pentagon?

We learn about all different types of shapes in geometry. One kind of flat shape is the polygon, also known as a plane figure, and it’s made of lines (sides) and corners where the lines connect. Plane figures are often named based on the number of sides and corners they have. A pentagon is a plane figure that has five sides and five corners.

Figure A: Pentagons have five sides and five corners.
Equilateral plane figure

The word pentagon contains Greek roots. When we break down the word into parts, penta means five and gon roughly means angles. An angle is where two lines come together and connect, so you can think of an angle as a corner of a shape. As you can see, the shape is named ‘pentagon’ because it has five angles, or corners!

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Types of Pentagons

This pentagon is a regular pentagon. We call it ‘regular’ because the sides are all equal in length. When the sides are equal lengths, we know that the angles are equal as well. That’s because when sides are equal distances from each other, their placement naturally creates equal-sized angles or corners. You can draw lines through a pentagon in five different places and divide it equally into two sections. These lines are called lines of symmetry.

But not all pentagons are regular. There are pentagons that have sides that are not all equal, and so they also have angles that are not equal. These are called irregular pentagons, since some sides and angles are bigger or smaller than the others. They do not have the lines of symmetry that a regular pentagon has.

Figure B: This pentagon is irregular because the sides are not equal in length and the angles are different sizes.
User created Pentagon

Real-World Examples

If you look around you, you can easily find common polygons, like squares, rectangles and even triangles. Pentagons are not as common, but you may have seen some and not even known that you were looking at a pentagon!

Some familiar examples of pentagons include the home plate used in baseball, the stitched shapes on a soccer ball and some road signs. Perhaps one of the most famous pentagons is the building in Washington, D.C., where our country’s defense department is located. When you look at it from above, you can see that it’s a pentagon.

The outside cover of soccer balls are often covered with black pentagons.
Pentagon shapes

Take a look around your home to see if you can find some real world examples of pentagons!

Lesson Summary

Pentagons are polygons that have five sides and five angles. They can be regular, where the sides and angles are equal in size, and they can also be irregular, where some of the sides and angles are different sizes. Pentagons are not as common in the real world as squares or rectangles, but you can find them if you look carefully.