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Perimeter Calculator
Work out the perimeter of seven common shapes, including the circumference of a circle.
Calculate perimeter
Perimeter: — units
Formula: —
How to use the Perimeter Calculator
- Choose the shape whose perimeter you want to calculate.
- Enter the measurements the shape needs in the input boxes.
- Read the perimeter and the formula that produced it.
Features
- Square, rectangle, triangle and circle
- Parallelogram, regular polygon and ellipse
- Formula shown next to every result
- Runs locally, no uploads
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Frequently Asked Questions
Common questions about the free online perimeter calculator.
The perimeter calculator handles squares, rectangles, triangles, circles, parallelograms,
regular polygons and ellipses.
The distance around a circle is called the circumference, and it equals two times pi times
the radius of that circle.
Add the length and the width together, then multiply by two, because a rectangle has two of
each of those sides.
Enter the length of one side and the number of sides. The perimeter is simply the side length
multiplied by that count.
An ellipse has no simple exact perimeter, so the tool uses Ramanujan's approximation,
which is accurate to a fraction of a percent.
Any single unit works, and the answer is given in that same unit, whether it is metres, feet
or anything else.
No. The perimeter is calculated entirely in your browser and nothing you type is sent to a
server.
Yes. The calculator is responsive and works in any modern browser on a phone, tablet or
desktop.
Last updated: October 10, 2026