Regular Octagon Perimeter Calculator

This regular octagon perimeter calculator works out the perimeter of a regular octagon, the eight-sided polygon with all sides equal. Because every side is the same length, the perimeter is simply the side length multiplied by eight, and the calculator returns it instantly along with the area as a bonus. Enter the side length, pick your unit, and read off the result. It is unit agnostic, so a side in metres gives a perimeter in metres and a side in centimetres gives a perimeter in centimetres. The perimeter is the total distance around the outside of the shape, which is useful for fencing, edging, trim, framing and border calculations as well as geometry work. There is nothing to look up and no trigonometry needed for the perimeter itself, since it is just eight equal sides added together. If you also need the area, that is shown beside the perimeter and explained on the matching area page. The formula, a worked example and the assumptions are set out below.

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Side length

Units

Side length6 m

Area

The formula

The perimeter of a regular octagon is the number of sides times the side length. In symbols, P = n s, where n = 8 and s is the side length. For comparison, the area is (1/4) n s² cot(pi/n).

Worked example

A regular octagon with a side of 6 has a perimeter of 8 times 6 = 48. Enter 6 above to confirm, and to see the matching area.

Frequently asked questions

How do you find the perimeter of a regular octagon?

Multiply the side length by eight. Every side of a regular octagon is the same length, so P = 8 times the side.

Is the perimeter the same as the circumference?

For a polygon we call the distance around the outside the perimeter. Circumference is the same idea but is the word used for a circle.

What if the octagon is irregular?

Then the sides differ, so add the individual side lengths instead. This calculator assumes a regular octagon with equal sides.

Who this calculator is for

This calculator is for students, tradespeople and designers who need the perimeter of a regular octagon for edging, framing or layout.