Perimeter of a Polygon Calculator

How to use the regular polygon perimeter calculator

What this calculator does

This calculator finds the perimeter – the total distance around the outside – of a regular polygon. A regular polygon has equal side lengths, so its perimeter is an exact multiplication: the number of sides multiplied by the length of one side. The tool is useful for geometry exercises, border and edging estimates, repeated panel layouts, craft templates, and quick dimensional checks. It does not calculate the perimeter of an irregular polygon whose side lengths differ; for that case, each individual side must be measured and added.

When to use it

Use it when you know that all sides are equal and need the full boundary length. Typical examples include finding the trim around a square sign, the edging around a regular hexagonal garden bed, the frame length for an octagonal panel, or the total length represented by a classroom geometry diagram. OpenStax's explanation of polygon perimeter and the formula for regular polygons provides the underlying rule used here.

How to calculate

1. The calculator opens with a ready-to-use demonstration: 8 sides, a side length of 17 inches, and an immediately available Excel workbook.
2. Replace Number of sides with the polygon's whole-number side count. A polygon must have at least three sides.
3. Enter the measured Side length. Use a positive number and a period for decimals, such as 3.5.
4. Choose the Length unit. When you switch units, the current side length is converted so the physical size stays the same.
5. Read Perimeter, the supporting values, the Calculation, and the detail table. Select Download Excel to export the current inputs and result.

Reset clears the demonstration and entered data, returns the unit to centimeters, removes calculated content, and may disable Download Excel until a complete valid polygon is entered again.

Input guide

Number of sides is required and accepts a whole number from 3 through 1,000,000; 8 is a realistic example. Increasing it increases the perimeter in direct proportion when side length stays fixed. Do not enter decimals, commas, words, or a value below 3. Side length is required and accepts a positive ordinary decimal up to 1,000,000,000; 17 is the demonstration value. A longer side increases the perimeter proportionally. Avoid decimal commas, scientific notation, negative values, and unit symbols inside the field. Length unit is required and offers millimeters, centimeters, meters, kilometers, inches, feet, yards, and miles. It changes the display and converts the current length; it does not change the actual polygon size. NIST's guide to SI units of length and their relationships is useful when checking metric conversions.

Output guide

Perimeter is the exact product of the accepted inputs, expressed in the selected length unit. Zero is not produced for a valid polygon because side length must be positive. A high or low value has no universal meaning; interpret it relative to the object or drawing you are measuring. Number of equal sides restates the validated side count. Side length restates one equal edge in the active unit. Calculation shows the exact multiplication used. In the table, Step names each operation, Value shows the current quantity or expression, and Explanation clarifies how that row contributes to the final boundary length. These outputs are identities from the regular-polygon model, not forecasts or recommendations.

Worked example

The opening example is a regular octagon with 8 sides, each 17 inches long. Apply the formula: perimeter = number of sides × side length. Therefore, 8 × 17 inches = 136 inches. The live result, summary pills, calculation table, and startup Excel workbook all show the same 136-inch perimeter. If the unit is changed to centimeters, 17 inches becomes 43.18 centimeters and the perimeter becomes 345.44 centimeters; the physical boundary is unchanged.