The length-to-width ratio is the proportional comparison between the longest and shortest dimensions of a fancy-shape diamond's outline, viewed from above. It is calculated by dividing the length by the width and is expressed as, for example, 1.50:1 or 2.00:1. The ratio is a primary aesthetic specification for fancy shapes - oval, marquise, pear, emerald, radiant, cushion - because outline proportions strongly influence the silhouette of the finished stone and its visual character.

Conventional ranges

The trade has settled on broad preferred ranges that vary by shape. For ovals, ratios from 1.30:1 to 1.50:1 are considered classic. Pears typically range from 1.45:1 to 1.75:1. Marquises favour 1.85:1 to 2.10:1. Emerald cuts run from 1.30:1 to 1.50:1. Radiants and cushions cluster around 1.00:1 (square) to 1.30:1 (rectangular). These are conventions, not grades; GIA and other major laboratories report the ratio as a measurement, not as a quality assessment, and the buyer's preference is the ultimate arbiter.

Ratios outside the conventional range are sometimes deliberately cut for design or yield reasons; a longer marquise reads more elongated, a squarer cushion has a heavier, more pillow-like feel. Buyers should view the actual stone before committing, since a ratio that reads well on paper may produce a less satisfying outline in person, particularly in pears and ovals where shoulder placement and tip alignment are not captured by the ratio alone.