What is the difference between perimeter and area?

Perimeter is the total distance around the outside of a shape, measured in linear units (meters, feet). Area is the amount of space inside the shape, measured in square units (m², ft²). Think of perimeter as the length of fence needed to enclose a yard, while area is the amount of grass inside.

How do you calculate the perimeter of an irregular shape?

For irregular shapes, measure each side individually and add all the lengths together. There is no shortcut formula — the perimeter is simply the sum of all outer edges. Use a ruler or measuring tape for physical objects, or coordinates for mathematical problems.

Is circumference the same as perimeter?

Yes, circumference is the specific term for the perimeter of a circle. While 'perimeter' applies to any shape, 'circumference' is used exclusively for circles and is calculated with C = 2πr or C = πd, where r is the radius and d is the diameter.

How do you find the perimeter of a triangle with only two sides?

You cannot find the exact perimeter with only two sides — you need all three. However, if you know two sides and the included angle, you can use the Law of Cosines to find the third side: c² = a² + b² - 2ab·cos(C), then add all three sides for the perimeter.

Perimeter Calculator

This perimeter calculator helps you find the perimeter (or circumference for circles) of any common geometric shape. Select your shape, enter the dimensions, and get instant results with detailed step-by-step calculations, formulas, and area as a bonus. Supports 10 different shapes with unit conversions between metric and imperial.

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calendar_today Updated: April 2026

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The Formula

The perimeter is the total distance around a two-dimensional shape. For circles, this is called the circumference. Each shape has its own formula based on its defining dimensions.

Rectangle: P = 2(l + w) | Square: P = 4s | Triangle: P = a + b + c | Circle: C = 2πr | Polygon: P = n × s

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Perimeter is always measured in linear units (m, cm, ft) — not square units

For circles, perimeter = circumference = 2πr ≈ 6.2832 × radius

Regular polygons: just multiply side length by the number of sides

For irregular shapes, measure and add all sides individually

Doubling all sides doubles the perimeter (linear scaling)

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Perimeter Calculator

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The Formula

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