Diamond cut grade

A cut grade rates the quality of the cutting, not the outline of the stone. GIA separates the two: a word like oval describes the shape, while cut describes the overall design, meaning how the facets and proportions are arranged to let light in and send it back to your eye. A standard round brilliant has 57 or 58 facets, and the 58th is the tiny flat facet at the bottom called the culet.

GIA's scale runs Excellent, Very Good, Good, Fair and Poor, and it applies to standard round brilliants in the D-to-Z colour range. GIA introduced it in 2006. Cut is one of the 4Cs, and it is easy to confuse with shape. For the outline itself, see the round brilliant cut.

GIA assesses seven components, which it groups into three. Face-up appearance covers brightness, fire and scintillation. Design covers weight ratio and durability. Craftsmanship covers polish and symmetry. The grade depends on how the proportions work together, including table size, crown angle and pavilion depth, which is the territory of diamond proportions.

GIA’s system took 15 years to develop and was tested against more than 70,000 human observations of real diamonds. The grade therefore rests on what viewers saw as well as on the geometry.

Cut is said to have the greatest impact on a stone's beauty. An expertly cut diamond can look brilliant even with lower colour and clarity grades, while a poorly cut diamond with top grades can look dull. AGS agrees that a well-cut diamond has more life and sparkle, and says a well-cut stone can even appear to have a better face-up colour or clarity.

That is why cut deserves attention before small steps in colour or clarity, which are often hard to see. Grades below Very Good show noticeable reductions in brightness or symmetry.

Most round brilliant diamonds on the market today receive Excellent or Very Good. It describes Excellent as delivering maximum brilliance and fire, and Very Good as great beauty at a lower price. Below Very Good, the grades show noticeable reductions in brightness or symmetry.

Before you decide, compare two or three stones of the same shape and similar weight under the same light. The grade summarises the cut, and your own eyes decide whether the gap between Excellent and Very Good is worth the price gap. If Excellent is within budget, it is the straightforward choice. If it would mean a smaller stone, weigh that against the short step down from Excellent to Very Good.

The round brilliant is the only shape that receives an official cut grade on its reports. Every other shape, such as the oval, pear, marquise, emerald, cushion and princess, is called a fancy shape, and GIA grades only its polish and symmetry.

This may change. In June 2026 Rapaport reported that GIA plans to launch cut grading for marquise, oval and pear diamonds in 2027, with details due in early 2027. Other laboratories have gone further: AGS Laboratories says it has extended its cut-grade methodology to fancy shapes such as oval, cushion, princess and emerald. AGS grades on a scale of 0 to 10 where 0 is the best, so its numbers run the opposite way to a score out of ten.

Until a cut grade exists for your shape, you judge cut by looking. Check the stone face-up for even brightness. In ovals and pears, look for the bow-tie effect, the dark bow-tie shaped shadow across the centre that GIA describes. If a diamond grading report lists polish and symmetry, read them as part of the answer. If you are planning a custom ring in a fancy shape, the design studio is a place to note the shape you want before you see stones.