Calculate the Perimeter of a Rectangle

The perimeter of a rectangle is the total length of its outline, i.e. the sum of its four sides. This calculator lets you calculate the perimeter of a rectangle or a square instantly, simply by entering the length and the width.

Rectangle perimeter formula

The formula for the perimeter of a rectangle is: P = 2 × (A + B), where A is the length and B is the width. Since the two pairs of opposite sides are equal, we add A and B, then multiply by 2.

For a square, since all sides are equal (A = B), the formula simplifies to: P = 4 × A.

How to calculate the perimeter of a rectangle?

The calculation is simple, in three steps:

• Measure the length A and the width B of the rectangle.
• Add the two values: A + B.
• Multiply the result by 2: P = 2 × (A + B).

Enter your values in the fields above and the perimeter is calculated automatically.

Perimeter calculation example

You want to fence a rectangular garden 12 meters long and 8 meters wide. To find out how many meters of fencing to buy, calculate the perimeter: 2 × (12 + 8) = 40 meters.

Another example: a room measuring 5.5 m by 3.2 m has a perimeter of 2 × (5.5 + 3.2) = 17.4 meters — useful for estimating a length of baseboard or wallpaper.

Which unit should I use?

Use the same unit of measurement for both sides. The perimeter is expressed in that same unit: meters give a perimeter in meters, feet give a perimeter in feet. No conversion is needed if you are consistent.

Visualize the shape of the rectangle

This calculator displays a proportional representation of the rectangle based on the entered values. This lets you visually check that the dimensions match the expected shape, particularly to distinguish a very elongated rectangle from a square.

Save your perimeter calculations

Press Save to keep the result in the history with the corresponding sides A and B. You can then export your data in CSV or PDF format to reuse it in a quote, a plan or a tracking table.