We highly recommend selecting the highest cut grade within your budget for a simple reason: of the Four Cs, no other characteristic has a greater influence on a diamond's appearance.
A diamond's cut grade is an objective measure of a diamond's light performance, or, what we generally think of as sparkle. When a diamond is cut with the proper proportions, light is returned out of the top of the diamond (which gemmologists refer to as the table). If it is cut too shallow, light leaks out of the bottom; too deep and it escapes out of the side.
Represents roughly the top 3% of diamond quality based on cut. Reflects nearly all light that enters the diamond. An exquisite and rare cut.
Represents roughly the top 15% of diamond quality based on cut. Reflects nearly as much light as the ideal cut, but for a lower price.
Represents roughly the top 25% of diamond quality based on cut. Reflects most light that enters. Much less expensive than a very good cut.
Represents roughly the top 35% of diamond quality based on cut. Still a quality diamond, but a fair cut will not be as brilliant as a good cut.
Diamonds that are generally so deep and narrow or shallow and wide that they lose most of the light out the sides and bottom. 1Diamond 1Heart does not sell diamonds with cut grades of poor.
For superior brilliance, choose a diamond with a Cut grade of Very Good or Excellent for round diamonds, and Good or better in fancy shape diamonds.
For those on a budget, primarily concerned with size, a diamond of Fair - Good cut may be an acceptable choice, especially in fancy shapes. While the diamond will lack the brilliance of a well cut diamond, it will allow a significant increase in size for the same price.