What is it?
The Perimeter Calculator finds the distance around a shape, such as for fencing or a border. It works for rectangles, squares, circles, triangles, regular polygons, ellipses and arcs.
Who is it for?
People buying fencing, borders, skirting or lights, gardeners, builders and students.
How to use it
Choose the Shape, fill in the sides, radius or Number of sides, and read the Perimeter (with Diameter, Area, Each inside angle or Arc length only where it applies). The answer appears as you type; there is no Calculate button. Tap Copy result to copy it, or Share on WhatsApp to send it.
Fencing and borders
- Subtract gate openings from the perimeter, then add 5–10% for joins and cutting waste.
- Fence posts: divide the length by the post spacing and add one. For a closed fence, posts = perimeter ÷ spacing.
- For an irregular plot, add all its measured sides; the perimeter of any polygon is the sum of its sides.
Circles and ellipses
- Circumference = 2 × π × radius. A 1 m wide round table has a 3.14 m edge.
- An ellipse has no simple exact formula. The tool uses Ramanujan’s approximation, which is accurate to a tiny fraction for any practical shape.
Errors and how to fix them
- “Enter the measurements” or “Those three sides cannot make a triangle”: as above.
- “A polygon has 3 or more sides”: set the number of sides to 3 or more.
Open the tool: Perimeter Calculator
Still stuck?
Contact support. Tell us which tool or page you were using, what you tapped, what you saw, and your phone or computer and browser (for example: Android phone, Chrome). We reply by email.
Questions, or an error not listed here?
Tell us in the comments: what you were doing, the exact message you saw, and your device and browser. We read every comment and add new fixes to this article.