GG.2 Identify polygons: up to 12 sides
What are polygons?
Polygons are flat, closed shapes made of straight sides. A shape must have at least three sides to be a polygon.
- 3 sides → triangle
- 4 sides → quadrilateral
- 5 sides → pentagon
A polygon cannot have curved sides or be open. All sides must connect to form a closed shape.
How to identify polygons by their sides
To identify a polygon, count the number of straight sides it has. Each number of sides has a special name.
- 6 sides → hexagon
- 8 sides → octagon
- 10 sides → decagon
Count carefully by tracing each side with your finger. Make sure you do not count the same side twice.
Common polygons up to twelve sides
Here are the names of common polygons students should know when counting up to twelve sides.
- 3 sides → triangle
- 4 sides → quadrilateral
- 5 sides → pentagon
- 6 sides → hexagon
- 7 sides → heptagon
- 8 sides → octagon
- 9 sides → nonagon
- 10 sides → decagon
- 11 sides → hendecagon
- 12 sides → dodecagon
Some names may be unfamiliar, but the rule is simple: the number of straight sides determines the polygon’s name.
How to describe polygons
When describing a polygon, you can talk about its number of sides, number of angles, and whether its sides are equal.
- “This shape has four equal sides, so it is a square.”
- “This shape has eight sides, so it is an octagon.”
- “This shape has six sides and six angles, so it is a hexagon.”
Remember: every side of a polygon meets another side at a corner, which is called a vertex.
Using polygons in real-world examples
Polygons appear all around us in everyday life. Recognizing them helps you connect math to the real world.
- A stop sign has eight sides → octagon
- A cracker might have six sides → hexagon
- A tile floor may use four-sided shapes → quadrilaterals
Not all real-world shapes are perfect polygons, but you can often identify the polygon they are closest to.