Dodecagon  (12-gon)
From Greek duo "two" + deka "ten" + gonia "angle"
Definition: A polygon with 12 sides
Try this Adjust the dodecagon below by dragging any orange dot. By clicking on the top left command line, you can switch it between a regular and irregular dodecagon.

Properties of regular dodecagons

Interior angle 150° Like any regular polygon, to find the interior angle we use the formula   (180n–360)/n . For a dodecagon, n=12. See Interior Angles of a Polygon
Exterior Angle 30° To find the exterior angle of a regular dodecagon, we use the fact that the exterior angle forms a linear pair with the interior angle, so in general it is given by the formula 180-interior angle. See Exterior Angles of a Polygon
Area 11.196s2
approx
Where S is the length of a side. To find the exact area of a dodecagon or any polygon, using various methods, see Area of a Regular Polygon and Area of an Irregular Polygon

Properties of all dodecagons

Number of diagonals 54 The number of distinct diagonals possible from all vertices. (In general  ½n(n–3)  ). In the figure above, click on "show diagonals" to see them. See Diagonals of a Polygon
Number of triangles 10 The number of triangles created by drawing the diagonals from a given vertex. (In general n–2). In the figure above, click on "show triangles" to see them. See Triangles of a Polygon
Sum of interior angles 1800° In general 180(n–2) degrees . See Interior Angles of a Polygon

Dodecagonal coins

Dodecagons are not seen much in everyday life. However, in Australia, there are coins in the shape of a dodecagon. Below is the 12-sided Australian 50 cent coin.

Related polygon topics

General

Types of polygon

Area of various polygon types

Perimeter of various polygon types

Angles associated with polygons

Named polygons

COMMON CORE

Math Open Reference now has a Common Core alignment.

See which resources are available on this site for each element of the Common Core standards.

Check it out