What is an Icosahedron? - Definition & Facts

Instructor: Rayna Cummings

Rayna has taught Elementary Education for 12 years (in both 1st, 2nd, and 3rd grades) and holds a M.Ed in Early Childhood Education from The Ohio State University

In this lesson, you will learn what an icosahedron is and explore the properties of this shape. You can even create your own icosahedron using things around your home. Now, let's go have some fun and learn all about icosahedrons!

What is an Icosahedron?

Have you ever heard of the shape called an icosahedron? An icosahedron is a polyhedron that has 20 faces, or flat surfaces. (A polyhedron is a 3-D shape with flat surfaces.)

An icosahedron has 20 flat sides.
Icosahedron example

Try to image an everyday object that's shaped like an icosahedron. It's hard, isn't it? That's because icosahedrons aren't very common. Well, if you've ever played a game that uses 20-sided dice, then you have seen a icosahedron! For example, the tabletop play role-playing game Dungeons uses 20-sided dice.

20-sided dice, like the red one in this image, are often used to play role-playing games.

Properties of Icosahedrons

Every shape has properties, or characteristics, that help you differentiate it from others. For example, a square has 4 sides and 4 corners, while a 3-D cube has 6 faces, 8 vertices (or corners) and 12 edges (the lines where the faces meet).

An icosahedron is a bit more complex. It has:

  • 20 equilateral triangle faces
  • 12 vertices (corners)
  • 30 edges

Let's Build An Icosahedron

The easiest way to learn about an icosahedron is to build one and see firsthand its 20 equilateral triangle faces, 12 vertices and 30 edges. For this activity, you will need some toothpicks and a bag of mini marshmallows as well as an image of an icosahedron for reference. Or, you can use a Geomag set--make your icosahedron using the rods in place of the toothpicks and the magnetic balls in place of the marshmallows.

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