What is Diamond Cut? The Complete Guide to Diamond Cut Grades and Quality

One of the 4Cs, a diamond's cut refers to how well it is proportioned and polished to maximize brilliance and fire. Cut is considered the most important C since it has the greatest influence on a diamond's sparkle and beauty. This guide will cover everything you need to know about diamond cut, from grading criteria to how it impacts value.

What Does Diamond Cut Mean?

A diamond's cut grade does not refer to its shape (round, oval, etc). Rather, it is an evaluation of how well the diamond is cut proportionally to optimize light performance.

Precise cutting and polishing are required to achieve ideal proportions and symmetry. This allows light to reflect and refract optimally off a diamond's precisely angled facets. When cut to ideal parameters, a diamond will have exceptional brilliance (white light reflection) and fire (spectral color dispersion).

The quality of the cut is a major factor that determines how beautifully a diamond interacts with light. A top-tier cut grade can make an average diamond look exquisite, while a poor cut can make even a large diamond appear dull.

5 Main Diamond Cut Grades

GIA (Gemological Institute of America) uses a cut grading system with 5 main categories, from best to worst:

Excellent

• Reflects nearly all light that enters. Exceptional brilliance and fire.
• Precisely cut within strict parameters to ideal proportions.
• Represents roughly the top 3% of diamond cuts.

Very Good

• Reflects nearly as much light as excellent cut diamonds.
• Well-cut within a reasonable margin of error from ideal proportions.
• Accounts for roughly top 15% of diamond cuts.

Good

• Reflects most light that enters. Adequate brilliance and fire.
• Cut somewhat outside the preferred parameters but still good overall.
• Represents approximately top 25% of diamond cuts.

Fair

• Noticeable light leakage due to variations in cutting.
• Below average brilliance and fire compared to ideal cut diamonds.
• Still a quality cut representing top 35-45% of diamond cuts.

Poor

• Significant light loss due to poor cutting. May appear dull.
• Well below average brilliance and fire.
• Cut represents the bottom 10% of diamonds.

While Excellent and Very Good represent well-cut diamonds, Good and Fair grades mean the diamond is cut too deep, shallow, or off-proportion. This reduces light return through the crown.

A Poor cut grade is significantly outside standard parameters. It causes major light leakage out the sides and bottom. A Poor cut should always be avoided as it negates the natural beauty of diamond.

See our diamond cut calculator

Diamond Cut Grading Criteria

Several factors are analyzed to determine a diamond's cut grade:

Proportions

• Table size - The width of the large top facet. Ideal is 53%-57% of diamond width.
• Crown height - Elevation from girdle to table. Ideal is 13%-16% of total height.
• Pavilion depth - Area under girdle down to culet. Ideal is 41%-44% of total depth.
• Culet size - Bottom point facet. Ideal is very small to none.

Symmetry

• The alignment and shape of all facets. Should be highly consistent.

Polish

• The overall smoothness and surface condition of the facets. Excellent polish shows no flaws under 10x magnification.

When a diamond is cut with excellent proportions, symmetry, and polish, the result is maximum brilliance and fire. Each factor is analyzed during grading.

The Anatomy of a Diamond

The parts of a diamond are designed to optimize interaction with light. Here are the key anatomical elements:

• Table - The large flat facet at the top.
• Crown - Upper section from table down to girdle.
• Girdle - The widest edge separating crown and pavilion.
• Pavilion - Bottom section from girdle down to culet.
• Culet - Small bottom facet.

The proportions, alignment, and polish of the crown, pavilion, table, and other facets are all considered when analyzing diamond cut quality.

Cut vs. Shape

Diamond cut and diamond shape are related but distinct terms. Shape refers to the diamond's outline form - round, oval, pear, etc. It is unrelated to cut grade. A round brilliant can be Poorly cut or Excellently cut.

Cut is an appraisal of how well a diamond is fashioned - its proportions, symmetry, and polish. It determines light performance, brilliance, and fire. So two diamonds of the same carat weight and shape can have vastly different cut grades and visual appeal.

How Does Cut Impact Diamond Value?

Along with carat weight, clarity, and color, cut quality is a primary driver of diamond prices. Diamonds with Excellent or Very Good cut grades command significant premiums over those with lower cut grades.

For example, a 1 carat round H-VS2 diamond may sell for:

• Excellent cut: $6,800
• Very Good cut: $6,200
• Good cut: $5,100
• Fair cut: $4,400
• Poor cut: $3,600

That's nearly a $3,000 difference between an Excellent and Poor cut of the same shape, carat weight, clarity and color!

Cut is so important because it has the greatest influence on a diamond's appearance and ability to scintillate brilliantly. Even if two diamonds share identical 4Cs, the one with superior cut will appear far more dazzling and fiery to the eye.

How to Choose a Well-Cut Diamond

• Start by selecting a shape you love like round, princess, cushion, etc.
• Then focus on choosing a GIA or AGS Excellent or Very Good cut grade.
• Review proportions to ensure table, crown, pavilion, etc. fall in ideal ranges.
• Verify excellent symmetry and polish under magnification.
• Compare diamonds of the same carat weight to see cut difference visually.
• Higher cut quality often offers better value than maximum size.

Diamond cutting expertise has improved enormously over the decades. Today, even budget-friendly diamonds can achieve high cut grades. With some education and diligence, finding a stunning well-cut diamond is within reach for every buyer.

Takeaway Tips

• Diamond cut assesses light performance - not shape.
• Excellent cut reflects most light and maximum brilliance.
• Proportions, symmetry and polish determine cut grade.
• Well-cut diamonds show exponentially more sparkle.
• Cut is a major driver of diamond prices and value.
• Focus on quality of cut before maximizing size.

Understanding diamond cut is key to selecting a stone that dazzles with optimal brilliance and fire. If you invest in an Excellent or Very Good cut, even an average diamond can look exquisite under the light. Let us know if you have any other questions about diamond cut in the comments!