How do you calculate the dimensions of a rectangle if you know the perimeter and the length?

A rectangle by definition has two pairs of sides with equal length. Since perimeter equals the length of all the sides. The equation for the perimeter of a rectangle could be thought of as: 2L + 2W = P Where L represents the length of one side of the rectangle and W represents the length of the adjacent (next to) side of the rectangle. If you know the length of one side and the perimeter, plug those values in as L and P and then solve for W. That will give you L and W which are the dimensions of the rectangle.