What is the formula for the perimeter of a regular octagon?

The perimeter of a regular octagon is P = 8s, where s is the length of one side. Because all eight sides are equal, you simply multiply the side length by 8.

Does this work for irregular octagons?

No. This calculator is for regular octagons only, where all sides are equal. For an irregular octagon you would need to add the lengths of all eight individual sides.

What units can I use?

You can enter the side length in millimeters, centimeters, meters, inches, feet, or yards. The perimeter result is returned in the same unit.

What is the interior angle of a regular octagon?

Each interior angle of a regular octagon measures 135 degrees. The sum of all interior angles is 1080 degrees.

How is a regular octagon different from a stop sign shape?

A stop sign is a regular octagon — all eight sides and all eight angles are equal. This calculator applies to any regular octagon, including stop-sign shapes.

Perimeter of an Octagon Calculator

Name: Perimeter of an Octagon Calculator
Availability: InStock
Author: Nham Vu

Enter the side length of a regular octagon and instantly get its perimeter using P = 8s.

Enter Side Length

Side Length (s)

Formula Used

P = 8 × s

where s is the side length of the regular octagon.

Result

Enter a side length and press Calculate

Octagon Diagram

Sides

Interior Angle

135°

Sum of Angles

1080°

Summary

Enter the side length of a regular octagon and instantly get its perimeter using P = 8s.

How it works

Enter the side length of the regular octagon.
Select the unit of measurement (mm, cm, m, in, ft, yd).
The calculator applies the formula P = 8s in real time.
The result is displayed in the same unit you selected.
Click "Copy Result" to copy the perimeter value to your clipboard.

Use cases

Find the total border length needed to frame an octagonal mirror or window.
Calculate fencing or trim material for an octagonal gazebo or deck.
Solve geometry homework problems involving regular octagons.
Verify hand calculations for construction or woodworking projects.
Convert octagon dimensions across different units of measurement.
Quickly check perimeter for tiled octagonal floor layouts.

Frequently Asked Questions

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