Decagon Calculator

Enter a side length from 0 (exclusive) to 1000000000. The calculator returns the area ((5 divided by 2) times side squared times the square root of (5 plus 2 times the square root of 5)), the perimeter (10 times the side), the apothem (side divided by (2 times tan(pi divided by 10))), and the circumradius (side divided by (2 times sin(pi divided by 10))). For example, a side of 5 gives area about 192.355221073, perimeter 50, apothem about 7.69420884294, and circumradius about 8.09016994375.

It uses perimeter = 10 x s, apothem = s / (2 x tan(pi / 10)), area = (1 / 2) x perimeter x apothem (equivalent to (5 / 2) x s^2 x square root of (5 + 2 x square root of 5)), and circumradius = s / (2 x sin(pi / 10)), where s is the side length you enter. This tool covers regular decagons with ten equal sides and equal interior angles of 144 degrees.

Enter a side length greater than zero through 1000000000. Decimal values are accepted. Zero, negative numbers, non-numeric text, and values above the limit show a clear error instead of a result.

Yes. The calculation and copy action run locally in your browser. CodeASystem does not upload or store the value you enter.