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
Number of Sides = (Sum of Interior Angles ÷ 180) + 2
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).
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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1728 Software Systems
