Pentagon Calculator

Calculate the properties of a regular pentagon from one side length.

Last updated: June 2026 | By Patchworkr Team

Regular Pentagon

Side Length

Math check: diagonal = phi x side, where phi = (1 + sqrt(5)) / 2

Result

Enter a side length to compute pentagon properties.

Formulas

A = s^2 sqrt(25 + 10 sqrt(5)) / 4

P = 5s

d = phi s

interior angle = 108 deg

If the side length is 6, the perimeter is 30 and the diagonal is about 9.708.

The interior angle of any regular pentagon is 108 degrees.

The pentagon diagonal has the golden ratio relationship only because the shape is regular.

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