Symmetry is the grading term used to describe the exactness of the shape and placement of facets on a diamond. There are many variations that affect the symmetry of a stone, including off-center culets and tables, poor facet alignment, misshapen facets, and non symmetrical girdles. With poor symmetry refraction (the bending of light) can be misdirected as it enters and exits the diamond, causing a decrease in the scintillation (sparkle) of the stone. Symmetry also plays an important role in displaying Hearts & Arrows. Without excellent symmetry, a diamond would be unable to display Hearts & Arrows due to the shape or location of the facets. Also, even with excellent or ideal symmetry, it does not necessarily mean the stone does in fact display Hearts & Arrows.

Symmetry is graded as: Excellent, Very Good, Good, Fair, or Poor, for stones graded by the Gemological Institute of America (GIA), and for stones graded by the American Gem Society (AGS), Ideal is also one of the grades, added above Excellent