If you know the area and width, use: length = area ÷ width
If you know the perimeter and width, use: length = perimeter ÷ 2 − width
If you know the diagonal and width, use: length = √(diagonal² − width²)
If you know the diagonal and length, use: length = the given length value
If you know the scale drawing, measure the corresponding side and convert using the scale
If you know the coordinates of two opposite corners, use the distance formula to find the side lengths
If you know one side and the perimeter, use: length = perimeter ÷ 2 − width