If the perimeter of a rectangle is known, finding the width is only possible if the length is also known. Infinite combinations of lengths and widths of a rectangle exist with any given perimeter.
The perimeter of a rectangle is given by the formula P = 2L + 2W, where P represents the perimeter, L represents the length and W refers to the width. If a given rectangle has a perimeter of 100 inches, the rectangle might have a width of 20 inches and a length of 30 inches. Two times 20 plus two times 30 does give a total perimeter of 100 inches. However, it is also possible that the width is 10 inches and the length is 40 inches.