Polygon Calculator

How to use

1. 1Pick the number of sides n. Use a preset (triangle, square, pentagon, hexagon, octagon, dodecagon) or type any whole number from 3 to 1000.
2. 2Choose which quantity you already know: side length s, apothem a, circumradius R, or total area A.
3. 3Type the value. Comma or period both work as the decimal separator. Scientific notation is accepted.
4. 4Pick the length unit. Every length output uses that unit; the area uses the unit squared.
5. 5Read side, apothem, circumradius, perimeter, and area in the Results panel, plus the four standard angles to the right.
6. 6Copy any value individually or click Copy summary to put the full report on your clipboard.

About this tool

Polygon Calculator solves every standard measurement of a regular polygon from one known value. Type the number of sides (n) and pick whether you know the side length s, the apothem a (center to the midpoint of a side), the circumradius R (center to a vertex), or the total area A. The tool derives every other quantity instantly using the canonical regular-polygon formulas: a = s / (2 tan(pi / n)), R = s / (2 sin(pi / n)), perimeter P = n s, and area A = (1/4) n s squared cot(pi / n). It also reports the four angle measures geometry classes and CAD work ask for most often: the interior angle (n - 2) times 180 / n, the exterior angle 360 / n, the central angle 360 / n, and the sum of interior angles (n - 2) times 180. The shape preview is drawn to scale on an SVG with the highlighted side, the apothem to that side, the circumradius to a vertex, the inscribed circle, and the circumscribed circle, so the geometry is easy to read at a glance. Length inputs accept a comma or a period as the decimal separator, and scientific notation. Length units are applied uniformly: every length output uses the chosen unit; the area uses the unit squared. A built-in preset row covers the common named shapes from equilateral triangle through dodecagon, and any integer from 3 to 1000 is accepted, which is enough to approximate a circle for layout work. Every result has its own Copy button, and Copy summary puts the full report on your clipboard. Useful for math homework, geometry refreshers, tile and paver layout, hex grid design, gazebo and trellis planning, sheet-metal fabrication, optics and reflector design, and any time one polygon property is known and the rest need to be derived. Everything runs in your browser; the values you enter are never uploaded and no signup is required. This is a math tool, not a CAD program; for fabrication, verify dimensions against your drawing tolerance.

Free to use. Works in your browser. No signup, no login.