Length to Width Ratio is a factor that is only important in the selection of a fancy cut diamond or a diamond in which the diameter is not round The measurements of round diamonds are always very near a 1 to 1 ratio. The length-to-width ratio is not a factor in accessing the shape of a round diamond. Measurements in a diamond are always calculated to the one-hundredth of a millimeter. The length-to-width ratio is calculated by dividing the length of the round diamond by the width. (Example) Round length equals 6.27 millimeters; round width equals 6.25 millimeters; 6.27 divided by 6.25 equals a length-to-width ratio of 1 to 1. Because round diamonds have little variation in the diameter, length-to- width ratio is not important.