Ideal Cut vs Excellent Cut: How to Choose a Diamond Cut Grade

What is the difference between an Ideal cut and an Excellent cut?

Cut is the only one of the 4Cs of diamond grading that is entirely in human hands. Colour, clarity and carat weight come from the rough crystal; cut is how well the cutter shaped and polished it to return light to your eye. A cut grade is a laboratory's summary of that work, and Ideal and Excellent are the labels at the very top.

Excellent is the highest cut grade GIA (the Gemological Institute of America) gives a round brilliant. Ideal is the highest grade at IGI (the International Gemological Institute) and at AGS (the American Gem Society), and at those labs Excellent is one step below it. So an IGI Ideal and a GIA Excellent are both top-of-scale stones, judged by different rulebooks. In practice, an Ideal grade usually means the angles and symmetry sit in a narrower window than the broad GIA Excellent band allows.

The word 'ideal' is also used loosely. Some sellers call a stone 'ideal cut' because of its proportions, with no lab grade behind it, and some brands sell 'super ideal' stones cut to an in-house standard. When you see the word, check whose grade it is. Our guide to how cut grades work explains the full scale from top to bottom. Cut grades only apply to brilliant-style faceting; an antique-style rose cut is judged differently, as our comparison of rose cuts versus brilliant cuts explains.

Which labs use Ideal and which use Excellent?

GIA introduced its cut grade for round brilliants in 2006, after years of research into how real people judge brightness and fire. It is deliberately broad: thousands of angle combinations can earn Excellent. IGI's scale adds Ideal on top, which splits off the tightest part of that range.

In Australia, most laboratory-grown diamonds come with IGI reports, and most natural diamonds above about half a carat come with GIA reports. That is why you see 'Ideal' far more often on lab-grown stones and 'Excellent' on natural ones. It does not mean lab-grown diamonds are cut better or worse; they are simply graded at a lab that uses a different top label. To see how the next grades down behave, read Excellent, Very Good and Good compared.

What proportions give a diamond an Excellent cut grade?

A cut grade comes from a handful of measurements on the report. The table is the flat top facet, given as a percentage of the diameter. Total depth is height divided by diameter. The crown angle is the slope of the top section, and the pavilion angle is the slope of the lower section, which does most of the work of bouncing light back up. The girdle is the thin edge around the widest point, and the culet is the tip at the bottom.

The angles have to suit each other. A 35° crown can look lively over a 40.8° pavilion but dark in the centre over a 41.6° one. This is why two GIA Excellent stones can look different side by side: one may sit in the centre of the range, the other near its edge. A stone graded Ideal, or a GIA Excellent with angles in the tight column above, is close to the classic proportions worked out by Marcel Tolkowsky in 1919 (about a 53% table, 34.5° crown and 40.75° pavilion), refined by later research.

Depth also changes how big the stone looks. A 1 carat round at about 61% depth measures roughly 6.4–6.5 mm across; the same weight at 64% depth may be closer to 6.2–6.3 mm, because more weight sits underneath where you cannot see it. Graders also check painting and digging, small changes to the upper and lower girdle facets that can add carat weight or shift the light pattern. Heavy painting or digging can pull a grade down even when the main angles look fine.

Can you see the difference between Ideal and Excellent cut?

A top cut grade is about three things. Brightness is the white light returned to your eye. Fire is the flashes of colour, from diamond splitting light into the spectrum. Scintillation is the sparkle and pattern of light and dark as the stone or your hand moves. Ideal and Excellent stones both score highly on all three.

Side by side under normal light, an IGI Ideal and a well-proportioned GIA Excellent usually look the same to most people. Where you can see a difference is at the edges of the Excellent band. Combinations of steep crown and deep pavilion angles can make the centre look darker, and shallow pavilions can leak light under the table, giving a glassy, watery look. These stones still grade Excellent, but they are not equal to the best of the grade.

Reflector tools make this visible. An ASET (Angular Spectrum Evaluation Tool) image colour-codes where a stone gathers light: red for bright direct light, green for softer light, blue for your own reflection, and black or white for light lost. A tight Ideal shows even red with a crisp, symmetrical pattern. Some very precisely cut rounds also show a hearts and arrows pattern in a special viewer: eight arrows from the top and eight hearts from below. It is a sign of excellent optical symmetry, though it is not part of any major lab's cut grade.

Size matters too. Below about 0.30 carat the facets are so small that the eye cannot separate an Ideal from a good Excellent. From around 1 carat, especially in a solitaire where the centre stone is the focus, precise angles become easier to appreciate.

Is a triple Excellent diamond the same as Ideal?

Triple Excellent (often written 3EX) means a GIA report shows Excellent for cut, polish and symmetry. Polish describes the surface finish of the facets; symmetry describes how accurately they line up and meet. Most stones IGI grades Ideal also carry Excellent polish and symmetry, so the two are close, but they are not identical. A 3EX stone can sit anywhere in GIA's broad Excellent window, while Ideal points to the tighter part of it.

Even a perfect set of grades leaves things out. A cut grade does not tell you:

• Where the angles sit within the range, which you need to read from the measurements.
• How the light actually returns, which an ASET image or a 360° video shows far better than a word.
• Whether inclusions block light, since a dark crystal under the table can reduce sparkle in any cut.
• Colour nuance: a strong cut cannot fix a stone with brown, grey or blue nuance, which can make a well-cut diamond look dull.
• Fluorescence, which is listed separately and in rare strong cases can make a stone look slightly hazy.

Do fancy shapes get an Ideal or Excellent cut grade?

Generally, no. GIA gives an overall cut grade only to standard round brilliants, and most labs treat fancy shapes the same way. On an oval, pear or cushion report, 'Excellent' refers to polish and symmetry, not cut. When a seller labels a fancy shape 'ideal', it is their own description. Our guide to judging cut in fancy shapes without a GIA grade explains what to look at instead: ratio, outline, bow-tie and light return.

Each shape has its own sensible proportions. A princess cut is judged on its square outline, depth and how evenly the crossed pattern lights up, while step cuts depend on clean, evenly spaced facets, as our emerald cut proportions chart shows.

Geometric shapes used as side stones, such as the shield, triangular and trapezoid cuts, or bullet cuts, are judged mostly on how well each pair matches in size, colour and brightness. Older and specialty styles, including the star cut, the Portuguese cut with its many tiers of facets, the Flanders cut and pentagonal stones, have no standard cut scale at all. For these, your eye and a gemmologist's view count for more than any grade.

Is an Ideal cut diamond worth paying more for?

Usually the price step between Ideal and a strong Excellent is small compared with a step in colour or clarity. The bigger jump is between Excellent and Very Good, or between a well-cut Excellent and one at the edge of the range. The figures below are indicative only, for a 1 carat round in G colour and VS2 clarity; actual prices move with the market and each stone.

Ideal tends to be the smart pick when:

• The stone is a round of 1 carat or more and will be the centre of attention.
• You care most about fire and crisp sparkle.
• The Ideal stone costs only a little more than the Excellent you are comparing.

An Excellent is usually all you need when the stone is small, set among other diamonds, or when your budget is better spent elsewhere. Cut affects sparkle more than a small clarity step does, so many people keep a top cut and save on clarity, as explained in when an SI1 makes sense and our look at VS1 versus VS2.

Natural vs lab-grown: is a diamond excellent cut grade the same for both?

Yes. Natural and laboratory-grown diamonds are the same material, with the same refractive index (about 2.42) and dispersion (about 0.044), so light behaves the same way in both. Labs apply the same cut scales to each, and an Ideal lab-grown round and an Ideal natural round perform alike.

What differs is the economics of cutting. Natural rough is costly, so cutters sometimes keep extra weight with a deeper pavilion or thicker girdle, which can push a stone down to Excellent or Very Good. Lab-grown rough costs much less, so cutters can more often favour light over weight, and top grades are very common. A natural Ideal round is a little harder to find and costs more, while a lab-grown Ideal costs much less than a natural stone of the same grades. Neither should be thought of as an investment; choose the stone you love wearing.

How to choose between an Ideal and Excellent cut diamond: step by step

1. Check the lab. Note whether the report is GIA, IGI or another lab, because 'Excellent' means the top grade at GIA but the second grade at IGI.
2. Confirm all three grades. Look for Excellent (or Ideal) cut with Excellent polish and symmetry.
3. Read the angles. Compare the crown angle, pavilion angle, table and depth with the tight range in the proportions table above.
4. Ask for light images or video. An ASET image or 360° video shows brightness and any dark or leaky areas.
5. Check the girdle and edges. A very thin girdle is more prone to chips and cavities near the edge.
6. Compare the price step. If Ideal costs only a little more, it is often worth it at 1 carat and above; if not, a strong Excellent is a sound choice.
7. See it in person if you can. Look at it under daylight and shop lighting, beside a stone a grade either side.

If any term on the report is new to you, our jewellery glossary explains it in plain English.