What is an ideal cut diamond?
By Jared James · Last updated 21 May 2026
Definition
An ideal cut diamond is one cut to a specific set of proportions designed to reflect the maximum amount of light back through the top of the stone, producing the brightness and fire that makes a diamond look its best. The proportions were originally calculated by mathematician Marcel Tolkowsky in 1919, and the term is still used today, particularly by AGS in its 0-to-10 grading scale where ideal is the top grade. On GIA certificates the equivalent is an Excellent cut grade, while the hearts and arrows pattern seen through a special scope is a sign of particularly precise faceting.
Frequently asked questions
- Is ideal cut the same as excellent cut?
- They describe the same quality but come from different grading systems. AGS uses the term ideal for its top grade, while GIA uses excellent. Both mean the diamond has been cut to proportions that maximise brilliance and light return.
- What are hearts and arrows in a diamond?
- Hearts and arrows is a pattern of optical reflections visible in a precisely cut round brilliant diamond when viewed through a specialised scope. Eight heart-shaped reflections appear from below and eight arrow shapes appear from above, indicating a high level of cutting symmetry. It is a sign of a very well-cut stone but is not a grading category in itself.
- Does an ideal cut make a diamond look bigger?
- It makes a diamond look brighter and more alive, and a brilliantly lit stone can appear larger than a poorly cut stone of the same carat weight. The cut affects how much light bounces back to your eye, so a well-cut smaller stone often outshines a poorly cut larger one.
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