Regular polygon calculator

Enter the number of sides and length of the regular polygon, and click "Calculate".
Number of Significant Digits>>>

The figure above is a regular octagon

The blue circle outside is called the circumcircle and the red circle is called the incircle.

Angle EAB is an inner angle

of the regular octagon

Angle EAF is an external angle of the regular octagon and it is equal to the central angle ACB.

AC is the radius of the circumcircle.

CD is the radius of the incircle.