Perimeter Calculator

Perimeter Calculator covers the shapes that come up when you are buying something sold by the length: fencing, skirting, edging, trim or guttering. Each shape has its own formula, and the working prints the one it used with your numbers in it.

Results come in metres and feet as well as your chosen unit, because length is the measurement most often needed in a different system from the one it was taken in. A room measured in centimetres still needs a figure in metres for ordering.

The ellipse is the interesting case. An ellipse's perimeter has no exact elementary formula -- it requires an elliptic integral -- so the calculator uses Ramanujan's approximation, which is accurate to better than one part in a million for any shape you would actually measure. The working says so rather than presenting it as exact.

The page shows its working, not just its answer. Where there is a formula it is printed with your own numbers substituted in, so you can check the result rather than take it on trust -- which is the difference between a calculator you can use for something that matters and one you cannot.

Everything runs inside your browser. What you type is never uploaded, never logged and never stored, and the calculator keeps working if your connection drops after the page has loaded.

• Shows perimeter, area, perimeter in metres, perimeter in feet and area per unit of perimeter together, so you are not running it twice
• Prints the formula with your own figures substituted in
• Updates as you type, with no button to press and no page reload
• Copy the result in one click
• Free, no sign-up, and it runs entirely in your browser

The perimeter calculator is used by writers, developers, students, marketers and anyone else who needs the job done once without installing software. Common cases include:

• Measuring for fencing or edging around a space
• Working out skirting board for a room
• Getting the circumference of a circular bed or pond
• Converting a perimeter between metres and feet