The geometric names for polygon shapes

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Regular Polygons

A list of regular polygons and their names. Polygons are figures composed of a number of straight lines that are joined together. Regular polygons have equal length sides and equal interior angles. Polygons are named according to their number of sides.

Often polygons with sides numbering greater then 10 are simply referred to n-gon (e.g. 17-gon) for convenience

No. of
sides
Polygon Name Internal Angle
3Triangle60
4Square or Quadrilateral90
5Pentagon108
6Hexagon120
7Heptagon128.571
8Octagon135
9Nonagon or Ennagon140
10Decagon144
11Hendecagon or Undecagon147.273
12Dodecagon150
13Triskaidecagon152.308
14Tetrakaidecagon154.286
15Pendedecagon156
16Hexdecagon157.5
17Heptdecagon158.824
18Octdecagon160
19Enneadecagon161.053
20Icosagon162
30Triacontagon168
40Tetracontagon171
50Pentacontagon172.8
60Hexacontagon174
70Heptacontagon174.857
80Octacontagon175.5
90Enneacontagon176
100Hectagon176.4
1000Chiliagon179.640
10000Myriagon179.964
100000Megagon179.996
10100Googolgonalmost 180 :-)

Intervening polygons

Polygons with sides numbering between the main divisions of ten above are named by combining the prefixes and suffixes listed below. For example a 56 sided polygon would be called a Pentacontakaihexagon.

No. of
Sides
Name Prefix   Name Suffix No. of
Sides
20Icosikai...combine with...henagon1
30Triacontakai......digon2
40Tetracontakai......trigon3
50Pentacontakai......tetragon4
60Hexacontakai......pentagon5
70Heptacontakai......hexagon6
80Octacontakai......heptagon7
90Enneacontakai......octagon8
...enneagon9
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