Cut versus shape
These two terms get confused. Shape refers to the outline (round, oval, princess). Cut refers to the quality of the proportions, symmetry, and polish of those facets — how well the diamond is engineered.
A round diamond and a princess diamond are different shapes. A well-cut round and a poorly-cut round are different cuts.
Why cut is supreme
Light enters a diamond through the table (top facet), reflects off the internal facets, and exits back through the top — creating brilliance and fire. This optical performance is entirely a function of cut precision.
A diamond with mediocre colour and clarity but excellent cut will outperform a diamond with perfect colour and clarity but poor cut. Cut quality is what makes diamonds look "alive."
How cut is graded
GIA grades cut on five levels: Excellent, Very Good, Good, Fair, Poor. The grade considers proportions (how the angles and facet sizes relate), symmetry (alignment of facets), and polish (surface finish).
We recommend never buying a round diamond below Excellent cut. For other shapes, GIA does not formally grade cut, but reputable sellers will provide proportion data so you can evaluate it.
Ideal cut
"Ideal" is a tighter standard than Excellent — typically reserved for diamonds whose proportions fall within the narrowest range for optimal light performance. Some retailers call it "Hearts & Arrows" when the symmetry is so precise that the pattern is visible under magnification.
For round diamonds, an Ideal cut is the gold standard. Expect to pay a 5–10% premium over Excellent.