This regular dodecagon has an area of 279.9 cm² and a perimeter of 60 cm.
Every interior angle is 150°; all twelve sum to 1800°. The exterior angle is 30°.
A regular dodecagon has 54 diagonals (12 × 9 / 2). They fall into five distinct lengths, from 9.66 cm (shortest) to 19.32 cm (longest, passing through the centre).
The incircle has area 273.48 cm²; the circumcircle has area 293.11 cm². The dodecagon fills 95.5% of its circumcircle.
Area scales as the square of side: doubling the side (5 cm) quadruples the area, while the perimeter only doubles.
Next stepSwitch the "Solve from" dropdown to work backwards from any known measurement, such as a required area or a given radius.