The cut of a diamond is arguably the most important factor affecting its overall appearance. Unlike the other Cs, which are based on a diamond's natural characteristics, the cut is determined by human craftsmanship. It directly influences the brilliance, fire, and scintillation of a diamond—that is, how well it reflects light.
Cut refers not to the shape (round, oval, princess, etc.), but to the quality of the diamond’s proportions, symmetry, and polish. A well-cut diamond will reflect light internally from one facet to another and then disperse it through the top, creating that signature sparkle. A poorly cut diamond, even with perfect clarity and color, may appear dull or dark.
The GIA grades diamond cuts for round brilliant diamonds on the following scale:
Only round brilliant cuts are given GIA cut grades, but other shapes (like emerald, cushion, or pear) are evaluated based on symmetry and proportions by other labs.
Even a flawless diamond with high carat weight and perfect color may look underwhelming if poorly cut. Cut maximizes a diamond’s beauty and should be prioritized if brilliance and sparkle are your main goals.