Perimeter Calculator

Calculate the perimeter or total boundary length of a rectangle, square, triangle or regular polygon. Enter the required side measurements, select a unit, and get the result with equivalent lengths in other common units.

Enter your shape measurements

Shape

Rectangle length / square side

Rectangle width

Triangle side A

Triangle side B

Triangle side C

The three sides must satisfy the triangle inequality: the sum of any two sides must be greater than the third.

Number of sides

Length of each side

This option assumes a regular polygon: all sides have equal length. For an irregular polygon, add every side length separately.

Measurement unit

All entered side lengths must use the selected unit.

Reset

Perimeter formulas for common shapes

Rectangle

Perimeter = 2 × (length + width)

Square

Perimeter = 4 × side length

Triangle

Perimeter = side A + side B + side C

Regular polygon

Perimeter = number of sides × side length

Example: rectangular boundary

A rectangular plot is 20 metres long and 12 metres wide. Its perimeter is:

2 × (20 + 12) = 64 metres

This is the total length around the outside of the rectangle. It can help estimate boundary fencing, edging or other perimeter materials. Actual material requirements may need extra allowance for gates, overlaps, corners and installation.

Example: triangular boundary

A triangle with side lengths of 3 m, 4 m and 5 m has a perimeter of:

3 + 4 + 5 = 12 metres

What if my polygon is irregular?

For an irregular polygon, the perimeter is still the sum of all outside side lengths. This calculator's polygon option assumes every side is equal. For an irregular shape, add the measured boundary segments manually or use a calculator designed to accept individual side lengths.

Frequently asked questions

What is perimeter?

Perimeter is the total distance around the outside boundary of a two-dimensional shape. It is measured in linear units such as metres, feet or centimetres.

Is perimeter the same as area?

No. Perimeter measures the boundary length, while area measures the amount of surface enclosed by that boundary. Perimeter uses units such as metres; area uses square units such as square metres.

Can I use this calculator for fencing?

Yes. Use the perimeter as an initial estimate of the boundary length. Deduct openings such as gates and allow for corners, overlaps and installation requirements before purchasing materials.

Does the polygon option work for an irregular shape?

No. It calculates a regular polygon using one repeated side length. For an irregular polygon, the length of every side must be added.

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