THE 4CS · 01 ROUND ONLY (GIA) 5 GRADES

Cut

How well a diamond's proportions, symmetry and polish work together to return light back through the crown.

Cut is the only one of the 4Cs that humans control entirely. A cutter starts with rough diamond and decides how to shape it — trading size for brightness, or fire for scintillation. GIA grades cut only for standard round brilliants, using Excellent, Very Good, Good, Fair and Poor.

The grade is not a single measurement. It combines proportions (table %, depth %, crown angle, pavilion angle), symmetry (how precisely facets align) and polish (how smooth each facet surface is). All three must be high for the stone to earn Excellent.

Cut has the largest single effect on a diamond's appearance of any 4C. A poorly-cut D Flawless stone can look dimmer than a well-cut H VS2. DiamondTheGuide only benchmarks Excellent and Very Good cut rounds.

GRADES
EX → PR
APPLIES TO
Round brilliant
IN FACET
EX + VG only
SHOWCASE · CROSS-SECTION VIEW Excellent

Excellent

Maximum brightness and fire. The stone returns nearly all entering light back through the crown.

Light return
Maximum return
Typical table %
54–57%
Typical depth %
59–62.3%
In DiamondTheGuide benchmarks
Yes

Illustration. Dashed lines show light paths — more exiting the crown = brighter stone.

Very Good

Slightly outside the ideal ranges but still very bright. Often indistinguishable from Excellent to the eye.

Light return
Strong return
Typical table %
53–58%
Typical depth %
58–63.5%
In DiamondTheGuide benchmarks
Yes

Illustration. Dashed lines show light paths — more exiting the crown = brighter stone.

Good

Noticeably less bright. Visible dark areas under standard lighting. Significant discount vs Excellent.

Light return
Moderate return
Typical table %
51–60%
Typical depth %
57.5–65%
In DiamondTheGuide benchmarks
Excluded

Illustration. Dashed lines show light paths — more exiting the crown = brighter stone.

Fair

Large dark areas, poor sparkle. Usually bought for very tight budgets. DiamondTheGuide excludes Fair and Poor from price benchmarks.

Light return
Poor return
Typical table %
47–65%
Typical depth %
56–67%
In DiamondTheGuide benchmarks
Excluded

Illustration. Dashed lines show light paths — more exiting the crown = brighter stone.

Poor

Poorly proportioned or finished stones. Light escapes through the sides and bottom. Excluded from DiamondTheGuide.

Light return
Very poor return
Typical table %
Any
Typical depth %
Any
In DiamondTheGuide benchmarks
Excluded

Illustration. Dashed lines show light paths — more exiting the crown = brighter stone.

The cut grade scale

GIA grades · round brilliants only

← BEST LIGHT RETURN · HIGHEST PRICE PREMIUM POOREST LIGHT RETURN →

What graders measure

GIA's cut model combines seven components across three categories. Each is measured on the actual stone and compared against thresholds derived from light-performance modelling of millions of proportions.

PROPORTIONS

Table %

Width of the table facet divided by average girdle diameter. Ideal: 54–57%.

Total depth %

Total height divided by average girdle diameter. Ideal: 59–62.3%.

Crown angle

Angle of the crown facets from the girdle plane. Ideal: 34–35°.

Pavilion angle

Angle of the pavilion facets. Critical for light reflection. Ideal: 40.6–41°.

Girdle thickness

Thin to slightly thick. Very thin girdles chip; very thick ones hide weight.

Culet size

Ideally none or very small. A large culet appears as a dark circle from above.

SYMMETRY

DiamondTheGuide alignment

Upper and lower half facets must meet precisely at the girdle.

Table centring

The table should sit centred over the culet.

Girdle roundness

For rounds, the girdle edge should be a true circle.

POLISH

Surface finish

Each facet surface is examined under magnification for polish lines, burns or abrasions.

DiamondTheGuide edges

Ridge lines between facets should be crisp and straight.

Three qualities of light

Cut determines how three distinct optical phenomena balance in a stone. A great cut maximises all three simultaneously — no other grade can do that.

Brilliance

White light reflected back through the crown. The overall brightness of the stone. Determined primarily by table % and pavilion angle.

Fire

Dispersion of white light into spectral colours — the rainbow flashes. Controlled by crown angle and crown height.

Scintillation

The pattern of light and dark areas as the stone or light source moves — the sparkle. A function of facet count, size and symmetry.

Cut and price

Excellent cut commands a premium over Very Good, and both sit well above Good and Fair. The gap is not as large as the colour or clarity premium for adjacent grades — but the visual difference is far greater.

DiamondTheGuide only shows benchmarks for Excellent and Very Good cut rounds. Fair and Poor are excluded because they represent a different product — stones where weight was preserved at the expense of beauty.

An Excellent cut 1.00 ct G VS1 round costs roughly [X]% more than the same spec in Very Good cut, based on [N] listings as of [DATE].

Explore cut grades in the explorer
Relative price premium by cut grade · 1.00 ct · G · VS1 · round Illustrative

Bar heights illustrate typical relative premiums only. Live values appear once the data feed is connected.

HOW FACET USES CUT

All price benchmarks in DiamondTheGuide are filtered to Excellent and Very Good cut grades only, for standard round brilliants graded by GIA or IGI. Fancy shapes do not carry an official cut grade — for those, DiamondTheGuide shows depth % and table % in the stone detail view so you can evaluate proportions yourself.

RELATED TERMS

Brilliant cutStep cutSymmetryPolishTable %Depth %GIAHearts and Arrows

Questions about cut

Is cut the most important of the 4Cs?

For most buyers, yes. Cut is the only grade entirely in the craftsman's control — nature determines color and clarity, but a cutter chooses the proportions. A well-cut I color, VS2 stone will out-sparkle a poorly-cut D, FL stone. DiamondTheGuide's price benchmarks only include Excellent and Very Good cut grades.

What is the difference between cut grade and cut shape?

"Cut grade" (Excellent, Very Good, Good…) describes how well the stone is proportioned and finished. "Cut shape" (round, oval, emerald…) describes its outline. GIA only issues cut grades for standard round brilliants. For fancy shapes, you evaluate proportions manually using length-to-width ratio, depth %, and table % ranges specific to each shape.

What is "Hearts and Arrows"?

A round brilliant with very precise facet alignment shows a pattern of eight hearts viewed from the pavilion and eight arrows viewed from the crown — visible through a special viewer. It's a signature of excellent optical symmetry. All H&A stones are Excellent cut, but not all Excellent cut stones show H&A. The premium is real but the practical brightness difference over a well-graded Excellent is very small.

Why do some Excellent cuts look dark in certain lighting?

Cut grade is measured under standard conditions. A stone optimised for maximum scintillation (contrast) can appear to have dark areas — called "contrast brilliance" — which is intentional and looks dramatic in diffuse light. Under spot lighting the same stone explodes with sparkle. Some buyers prefer this look; others want the uniform brightness of a "spread" cut.

Can a lab-grown diamond have a better cut than natural?

Yes, and it often does. Lab-grown rough is more predictable in shape and has fewer natural imperfections to cut around. Cutters can target ideal proportions without the same financial pressure to preserve weight. Lab-grown stones are graded on the same cut scale by GIA and IGI.

Does cut affect a diamond's apparent size?

Yes. A stone cut with a large table and shallow pavilion can have a larger face-up diameter than an Excellent cut of the same carat weight — but it will look dimmer. A too-deep stone hides weight in the bottom and looks smaller face-up. Excellent cut rounds optimise both: maximum brightness and a diameter appropriate for their weight.