The length-to-width ratio is a comparison of the length and the width of a fancy shape diamond. This ratio expresses how relatively long or wide a diamond appears when viewed from the top. Each of the fancy shapes (princess, Asscher, marquise, emerald, radiant, cushion, oval, pear, heart) has a certain length-to-width ratio that is considered most appealing for that shape, however, personal preference prevails, and some may prefer a shorter, wider outline; or longer, thinner shape.
The length-to-width ratio is calculated by dividing the length of the diamond by its width. For example, a princess-cut diamond that is 5.45mm long and 5.30mm wide, has a length-to-width ratio of 1.03. This diamond would appear perfectly square to the eye. Whereas a marquise-cut diamond that is 6.10mm long and 2.95mm wide would have a length-to-width ratio of 2.07 and when viewed from the top, it would appear to be about twice as long as it is wide.