Regular Polygon Calculator
Scroll down for Instructions and Definitions

Input data in the first 2 boxes on the right, then click 'Calculate'.

Sum of Interior Angles = (Number of Sides -2) • 180 degrees

Each Exterior Angle = Each Central Angle = (360 degrees) ÷ (Number of Sides)

Polygon Names
Sides     Name Sides     Name Sides     Name
    3     triangle     9     nonagon   15     pentadecagon
    4     quadrilateral       10     decagon   16     hexadecagon
    5     pentagon   11     hendecagon   17     heptadecagon
    6     hexagon   12     dodecagon   18     octadecagon
    7     heptagon   13     tridecagon   19     enneadecagon    
    8     octagon   14     tetradecagon       20     icosagon
Regular Polygons

This calculator works only for regular polygons - those polygons which have ALL sides equal & ALL interior angles equal.
The above figure shows a regular octagon.
The outer circle surrounding it is called a circumscribed circle (or circumcircle) and the inner circle which is surrounded by the octagon is called the inscribed circle (or incircle).
Angle EAB is one of the 8 interior angles.
Angle EAF is one of the 8 exterior angles and equals central angle ACB.
Line AC is called the circumradius (the radius of the outer, circumscribed circle).
Line CD is called the inradius or the apothem (the radius of the inscribed circle).

Significant Figures >>>
The default setting is for 5 significant figures but you can change that by inputting another number in the box above.

Answers are displayed in scientific notation and for easier readability, numbers between .001 and 1,000 will be displayed in standard format (with the same number of significant figures.)
The answers should display properly but there are a few browsers that will show no output whatsoever. If so, enter a zero in the box above. This eliminates all formatting but it is better than seeing no output at all.

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