Perimeter of a Rectangle

The perimeter of a rectangle is found by adding the lengths of its four sides. It is twice the sum of its length l and width w because the opposite sides of a rectangle are equal.

Although arbitrary, the length is usually defined as the rectangle's longer sides and the width its shorter sides.

Proof

Consider a rectangle ABCD with side lengths l and w. Recall that a rectangle has two pairs of equal sides: the top and bottom sides (length) and the left and right sides (width).

The perimeter P of the rectangle is the sum of all its sides. P = l + w + l + w Combining like terms results in the formula.

P=2 l + 2w