Choose any regular polygon from triangle to dodecagon. Enter a side length or circumradius and instantly get area, perimeter, apothem, and interior angles — with full step-by-step work.
Circumradius R = s / (2 sin(π/n))
Apothem a = s / (2 tan(π/n))
Area = ½ · a · P where P = n·s
Interior angle = (n−2)·180° / n
If R is given instead: s = 2R·sin(π/n), then apply the same formulas for apothem and area.
The circumradius is the distance from center to vertex; the apothem is center to midpoint of a side.
A tutor can walk through every formula and show you how they connect — with clear diagrams and practice problems.