An octagon is a polygon that has eight sides. The internal angles of a regular octagon is 135°. The shape of a "STOP" sign is a regular octagon, as this makes it easy to recognise even when it is covered in dirt or snow.

regular	irregular	concave	complex

In architecture, an octagon house is a house built in an octagonal shape. Monticello is the most famous example.

In mixed martial arts, The Octagon is the name of the octagonal ring used in the Ultimate Fighting Championship, and by metonymy a term for the UFC itself as well.

See also: octagonal number

External links

• How to calculate the sides of a octagon using Microsoft Windows calculator. http://buster2058.netfirms.com/octagon/octagon.htm