A rectangle is a parallelogram with a right angle.

Note that in a rectangle the opposite sides are congruent (equal in measure).

Given the following:

l: The length of the rectangle

w: The width of the rectangle

P: The perimeter of the rectangle

A: The area of the (interior of the) rectangle

P = 2l + 2w    or    P = 2(l + w)

A = lw²

Note that in many cases the length is usually the longest side and the width is the shortest side [i.e. l > w].

In mathematics the length is the measure of one of two parallel sides and the width is the measure of one of the other two parallel sides [i.e. the length does not have to larger than the width.]