A decagon is a polygon with exactly ten sides. A regular decagon has all ten sides equal in length and all ten interior angles equal to 144°.

What is the formula for the perimeter of a decagon?

The perimeter of a regular decagon is P = 10 × s, where s is the length of one side. Because all sides are equal, you simply multiply the side length by 10.

Does this work for irregular decagons?

No. This calculator assumes a regular decagon where all ten sides are the same length. For an irregular decagon, add the lengths of all ten sides individually.

What unit should I use?

Use whatever unit your measurements are in — the calculator supports millimeters, centimeters, meters, inches, feet, and yards. The result uses the same unit you selected.

What is the interior angle of a regular decagon?

Each interior angle of a regular decagon measures 144°. The sum of all interior angles is (10 − 2) × 180° = 1440°.

Perimeter of a Decagon Calculator

Enter the side length of a regular decagon and instantly get its perimeter (10 × side length).

Decagon Side Length

Side Length (s)

Unit

Formula

P = 10 × s

Enter a side length and click Calculate.

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Summary

A regular decagon is a ten-sided polygon where all sides are equal in length and all interior angles are equal (144° each). Its perimeter is simply ten times the length of one side. This calculator lets you enter a side length in any unit and instantly returns the perimeter.

How it works

Enter the side length of your regular decagon in the input field.
Select the unit of measurement (mm, cm, m, in, ft, or yd).
The calculator applies the formula P = 10 × s.
The perimeter is displayed instantly along with a visual diagram.
Copy the result with one click.

Use cases

Calculate material needed to frame a decagonal window or mirror.
Find the fencing length for a ten-sided garden bed.
Solve geometry homework involving regular polygons.
Verify architectural measurements for decagonal floor plans.
Compute trim length for decorative decagonal tiles.
Cross-check CAD software polygon dimensions.
Determine the border length of a decagonal table or surface.
Estimate edging material for a ten-sided landscape feature.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu