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Polygon Perimeter Calculator | Find Perimeter From Side Length

Find the perimeter of any polygon — regular or irregular — from its side lengths, with interior angles for regular shapes. Enter the sides and get the total boundary length, ideal for fencing, framing and geometry.

Last updated: July 2026 · Free · No sign-up required

Results

Enter values above and click Calculate to see your result instantly.

What the Perimeter Of Polygon Calculator does

Every result on this page comes from a real formula — P = n × a; apothem = a ÷ (2tan(π÷n)); A = P × apothem ÷ 2 — computed live in your browser the moment you press the button.

Scroll past the calculator for a quick-reference table, a step-by-step methodology with a fully worked example, and answers to the questions people most often ask about perimeter of polygon calculator.

Quick reference

Polygon (side 5)PerimeterArea
Triangle (3)1510.83
Square (4)2025
Hexagon (6)3064.95
Octagon (8)40120.71

info Perimeter Of Polygon Calculator

Free math calculator — enter your numbers and get an instant, accurate result.

info Private by design

Everything runs locally in your browser. No uploads, no accounts, no tracking.

info Works everywhere

Fully responsive and mobile-friendly — calculate on any device, any time.

info Educational

Includes the formula and step-by-step explanation so you understand the math, not just the answer.

Interpretation guide

OutputMeaning
PerimeterTotal edge length — fencing/trim needed
ApothemCentre to edge midpoint — key to area
Interior angle(n−2)×180÷n — corner angle for cuts

lightbulb Worked example

Let's say you are using the Perimeter Of Polygon Calculator. Calculates perimeter of polygon using P = n × a, live in your browser. Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula P = n × a; apothem = a ÷ (2tan(π÷n)); A = P × apothem ÷ 2 and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: P = n × a; apothem = a ÷ (2tan(π÷n)); A = P × apothem ÷ 2

The Perimeter Of Polygon Calculator is built on a well-established calculation method. It uses the formula P = n × a; apothem = a ÷ (2tan(π÷n)); A = P × apothem ÷ 2 to turn your inputs into a reliable result. Calculates perimeter of polygon using P = n × a, live in your browser. The steps are shown on the page so you can follow the reasoning from input to output.

  1. Enter the number of sides n (3 or more) and the side length a.
  2. Perimeter is simply n × a.
  3. The apothem a÷(2tan(π÷n)) and area P×apothem÷2 are computed for the same shape.
  4. The interior angle (n−2)×180÷n helps with mitre cuts.

Example: a hexagon with side 5 → P = 30, apothem 4.33, area 64.95, corners 120°.

Authoritative source: Wolfram MathWorld

Frequently asked questions

How do you find the perimeter of a polygon?
Enter the required values into the input fields and press the calculate button. The tool applies the formula P = n × a; apothem = a ÷ (2tan(π÷n)); A = P × apothem ÷ 2 and returns the result with a short explanation of each step, so you can check the working yourself.
What is an apothem?
The Perimeter Of Polygon Calculator is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Calculates perimeter of polygon using P = n × a, live in your browser. There is no limit on usage, and it works on any device.
Does this work for irregular polygons?
Yes — the calculator accepts the side lengths of any polygon, regular or irregular, and sums them for the perimeter. For irregular shapes you enter each side length; for regular polygons you enter one side and the number of sides, and the tool multiplies. The distance-between-vertices mode also handles polygons defined by coordinates.
What is the interior angle of my polygon?
The interior angle sum of any n-sided polygon is (n − 2) × 180°. For a regular polygon, each interior angle is (n − 2) × 180° ÷ n: a regular hexagon has angles of 120° and a regular pentagon 108°. The calculator reports the per-angle value for regular polygons and the total angle sum for any polygon.
Is this polygon calculator free?
Yes — the Perimeter Of Polygon Calculator. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.
What's the fastest way to get a square's perimeter?
Multiply one side by 4 — a 15 ft side means 60 ft of fence line. Working backwards from area: side = √area, so a 225 sq ft square patio has 15 ft sides and a 60 ft perimeter. The same shortcut generalizes to any regular polygon: perimeter = side × number of sides.
What does the Perimeter Of Polygon Calculator do?
Calculates perimeter of polygon using P = n × a, live in your browser. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.
What formula does the Perimeter Of Polygon Calculator use?
The Perimeter Of Polygon Calculator applies the standard formula: P = n × a; apothem = a ÷ (2tan(π÷n)); A = P × apothem ÷ 2. The tool walks through each step of the calculation so you can verify the numbers yourself.
Is the Perimeter Of Polygon Calculator free and private?
Yes — it is free with no sign-up or limits, and all calculations run in your browser so no measurements are uploaded. CalcaTools funds itself with display ads. The tool computes perimeters for regular and irregular polygons, plus interior angles for regular ones.
How accurate is the Perimeter Of Polygon Calculator?
The Perimeter Of Polygon Calculator applies the standard formula: P = n × a; apothem = a ÷ (2tan(π÷n)); A = P × apothem ÷ 2. It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

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