Regular Polygon Calculator

Calculate angles, area, and perimeter of any regular polygon from a triangle to a dodecagon

Interior angle = (n−2)×180°/n = (6−2)×180°/6 = 120°
Interior angle
120°
Exterior angle
60°
Perimeter
30
Apothem
4.3301
Area
64.9519
5120°60°

About this calculator

The Regular Polygon Calculator computes interior angles, exterior angles, area, perimeter, and apothem for any regular polygon from a triangle to a 20-sided figure. Enter the number of sides and side length to instantly see all properties. Great for geometry, architecture, and understanding how polygons scale.

Common examples

  • Equilateral triangle (3 sides), side = 6 cm → Area ≈ 15.59 cm², Perimeter = 18 cm, Interior angle = 60°
  • Square (4 sides), side = 5 m → Area = 25 m², Perimeter = 20 m, Interior angle = 90°
  • Regular pentagon (5 sides), side = 4 cm → Area ≈ 27.53 cm², Perimeter = 20 cm, Interior angle = 108°
  • Regular hexagon (6 sides), side = 3 cm → Area ≈ 23.38 cm², Perimeter = 18 cm, Interior angle = 120°
  • Regular octagon (8 sides), side = 2 m → Area ≈ 19.31 m², Perimeter = 16 m, Interior angle = 135°