A nonagon (also called an enneagon) is a polygon with exactly nine sides. A regular nonagon has all nine sides equal in length and all nine interior angles equal to 140°.

What is the formula for the perimeter of a nonagon?

The perimeter of a regular nonagon is P = 9 × s, where s is the length of one side. Because all sides are equal, you simply multiply the side length by 9.

Does this work for irregular nonagons?

No. This calculator assumes a regular nonagon where all nine sides are the same length. For an irregular nonagon, add the lengths of all nine 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 nonagon?

Each interior angle of a regular nonagon measures 140°. The sum of all interior angles is (9 − 2) × 180° = 1260°.

Perimeter of a Nonagon Calculator

Enter the side length of a regular nonagon and instantly get its perimeter (9 × side length).

Nonagon Side Length

Side Length (s)

Unit

Formula

P = 9 × s

Enter a side length and click Calculate.

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Summary

A regular nonagon is a nine-sided polygon where all sides are equal in length and all interior angles are equal (140° each). Its perimeter is simply nine 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 nonagon in the input field.
Select the unit of measurement (mm, cm, m, in, ft, or yd).
The calculator applies the formula P = 9 × 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 nonagonal window or mirror.
Find the fencing length for a nine-sided garden bed.
Solve geometry homework involving regular polygons.
Verify architectural measurements for nonagonal floor plans.
Compute trim length for decorative nonagonal tiles.
Cross-check CAD software polygon dimensions.

Frequently Asked Questions

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