Calculators
Pentagon Calculator
Calculate regular pentagon area, perimeter, apothem, and diagonal from a side length locally in your browser.
Enter a side length from 0 (exclusive) to 1000000000 to see the area ((1/4) × √(5(5 + 2√5)) × s²), perimeter (5 × s), apothem (s ÷ (2 × tan(36°))), and diagonal (φ × s). The calculation runs locally in your browser; your value is not uploaded or stored.
Find regular pentagon measurements without uploading anything.
Enter a side length from 0 (exclusive) to 1000000000 to see the area, perimeter, apothem, and diagonal. Everything runs locally in your browser, so your value is not uploaded or stored.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
What does the pentagon calculator show?
Enter a side length from 0 (exclusive) to 1000000000. The calculator returns the area ((1 divided by 4) times the square root of 5 times (5 plus 2 times the square root of 5), times side squared), the perimeter (5 times the side), the apothem (side divided by (2 times tan(36 degrees))), and the diagonal (the golden ratio times the side). For example, a side of 5 gives area about 43.0119350147, perimeter 25, apothem about 3.44095480118, and diagonal about 8.09016994375.
Which formulas does the pentagon calculator use?
It uses area = (1 / 4) x square root of (5 x (5 + 2 x square root of 5)) x s^2, perimeter = 5 x s, apothem = s / (2 x tan(pi / 5)), and diagonal = ((1 + square root of 5) / 2) x s, where s is the side length you enter. This tool covers regular pentagons with five equal sides and equal 108-degree interior angles.
Which inputs are accepted?
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.
Do my numbers stay private?
Yes. The calculation and copy action run locally in your browser. CodeASystem does not upload or store the value you enter.