BYTETOOLS

Perimeter Calculator

Work out the perimeter of a rectangle, square, triangle, trapezoid, parallelogram, regular polygon, circle or ellipse in metric or imperial units.

16
Perimeter (m)

Formula

P = 2(l + w) = 2(5 + 3)

P = 16 m

What is the Perimeter Calculator?

The ByteTools Perimeter Calculator measures the distance around eight plane shapes: rectangle, square, triangle, circle, ellipse, trapezoid, parallelogram and any regular polygon from 3 to 1,000 sides.

  • Eight shapes including ellipse and regular n-gon
  • Metric and imperial units (m, cm, ft, in, yd)
  • Ramanujan approximation for the ellipse, clearly labelled
  • Triangle inequality check catches impossible side sets
  • Formula shown for every calculation
  • 100% private — runs entirely in your browser

How to use the Perimeter Calculator

  1. 1

    Select a shape — rectangle, square, triangle, circle, ellipse, trapezoid, parallelogram or regular polygon.

  2. 2

    Choose your measurement unit.

  3. 3

    Enter the side lengths, radius or axes the shape requires.

  4. 4

    Read the perimeter and the formula used below it.

  5. 5

    Click Copy to grab the result.

About the Perimeter Calculator

The ByteTools Perimeter Calculator measures the distance around eight plane shapes: rectangle, square, triangle, circle, ellipse, trapezoid, parallelogram and any regular polygon from 3 to 1,000 sides. Choose the shape, enter its side lengths or radii in metric or imperial units, and the perimeter appears instantly with the formula written out.

Perimeter is the number you need for fencing a garden, edging a lawn, framing a picture or adding trim to a room — as well as for geometry homework. The ellipse uses Ramanujan's celebrated approximation, since an ellipse has no exact closed-form perimeter; for everyday axis ratios its error is far below 0.01%, and the tool says so honestly next to the result.

Everything is calculated locally in your browser. No values are uploaded or stored, so it is fast, private and works offline.

Frequently asked questions

How do you calculate the perimeter of a rectangle?

Add the length and width, then double the sum: P = 2(l + w). A 5 × 3 room needs 2 × 8 = 16 units of trim. The calculator applies the same idea to every straight-sided shape by summing its sides.

Is circumference the same as perimeter?

Yes — circumference is simply the name given to the perimeter of a circle. It is calculated as C = 2πr, so a circle with a 5 m radius has a circumference of about 31.42 m. This tool computes it under the Circle option.

Why is the ellipse perimeter an approximation?

Unlike a circle, an ellipse has no exact closed-form perimeter — the true value is an elliptic integral that cannot be written with elementary functions. This tool uses Ramanujan's approximation, P ≈ π[3(a + b) − √((3a + b)(a + 3b))], which is accurate to better than 0.01% unless the ellipse is extremely elongated.

How do I find the perimeter of a regular polygon?

Multiply the number of sides by the side length: P = n × s. A regular hexagon with 4 cm sides has a perimeter of 24 cm. The calculator accepts any regular polygon from a triangle up to 1,000 sides.

Can I use this to work out how much fencing I need?

Yes — the perimeter of your garden or yard is exactly the fence length required. Measure each side, pick the matching shape (or use the trapezoid for four unequal sides), and add a small allowance for gates, posts and cutting waste.

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