Polygon with twelve sides.
- A dodecagon is a regular dodecagon if all its sides are congruent and if all its interior angles are congruent.
- A dodecagon has twelve interior angles; if it is a regular dodecagon, each of its interior angles measures 150°.
The formula to calculate the area A of a regular dodecagon of side length c is:
- The figure below is a regular dodecagon. The segment a represents its apothem.
- This is an irregular and non-convex dodecagon: