Diamond Education

Diamond Cut

Of the 4Cs, cut is the only one that is about craftsmanship rather than the rough crystal, and it is the one that decides whether a diamond sparkles.

By 25karats · Updated 2026 · 7 minute read

Color, clarity, and carat describe the stone nature produced. Cut describes what a human being did with it, and it has more effect on how a diamond looks than the other three combined.

A poorly cut diamond with a flawless grade and perfect color still looks dull. A superbly cut stone two color grades lower will outshine it across a room. If your budget forces a compromise, make it anywhere but here.

What cut actually controls

Light enters a diamond through the table, bounces off the pavilion facets, and returns to your eye. Cut determines how much of it comes back and how it looks when it does.

Brilliance: the white light returned through the table. Too shallow and light escapes out the bottom; too deep and it leaks out the sides.
Fire, light split into rainbow colors as it refracts. This is what makes a diamond flash color rather than just gleam.
Scintillation: the sparkle that appears as the stone or the light moves, produced by the pattern of bright and dark facets.

Cut is not the same as shape. Shape is the outline: round, oval, pear. Cut is the quality of the proportions and finish within that outline. A round diamond and an oval are different shapes; two round diamonds can be worlds apart in cut. See our diamond shapes guide.

Diamond anatomy

Grading reports use a specific vocabulary for the parts of a stone. These are the terms worth knowing.

Table: The large flat facet on top, and the main window for light.
Crown: The upper portion, from the table down to the girdle.
Girdle: The narrow band around the widest point, where prongs grip.
Pavilion: The lower cone, which reflects light back up.
Culet: The point or tiny facet at the very bottom.
Depth: Table to culet, given as a percentage of the diameter.
Diameter: The width across the girdle: the size you actually see.

The cut grade scale

GIA grades round brilliants on five levels. IGI uses the same five for round diamonds.

Grade	What it means	Our recommendation
Excellent	Maximum light return; the proportions are right	Buy this
Very Good	Very close to Excellent, and hard to tell apart by eye	A sensible way to save
Good	Noticeably less lively, though still attractive	Only if budget demands it
Fair	Visibly dull compared with the grades above	Avoid
Poor	Substantial light leakage; looks lifeless	Avoid

Buy Excellent, or Very Good if you need the money elsewhere. The gap between Excellent and Very Good is subtle. The gap between Very Good and Good is not, and below Good a diamond stops doing the one thing it is for. Cut is the last place to economize, drop a color or clarity grade instead.

The numbers behind the grade

If you like to check the report yourself, these are the ranges most commonly associated with top-performing round brilliants. Treat them as a sanity check rather than a rule: the overall grade accounts for how the proportions work together.

Measurement	Typical range for a top cut	What goes wrong outside it
Table %	54 – 58%	Too large loses fire; too small loses brilliance
Depth %	59 – 62.5%	Too deep hides weight below the girdle; too shallow leaks light
Girdle	Thin to slightly thick	Extremely thin chips easily; extremely thick wastes weight
Polish & symmetry	Excellent or Very Good	Poor finish scatters light and dulls the surface
Culet	None or very small	A large culet shows as a dark spot through the table

You may also see hearts and arrows advertised: a pattern visible under a special viewer that indicates exceptional optical symmetry. It is a genuine mark of precision cutting, and it carries a premium. It is not a requirement for a beautiful stone.

Why fancy shapes have no cut grade

This surprises most buyers: only round brilliants receive a cut grade from the major laboratories. There is no internationally accepted system for grading the light performance of ovals, pears, emeralds, or any other fancy shape.

Reports on fancy shapes still give polish and symmetry grades, plus the measurements, but the overall “how well does this sparkle” verdict is absent.

What to do instead. For a fancy shape, judge it yourself: look for even light return with no dark zones, check the length-to-width ratio suits your taste, watch for the bow-tie in elongated shapes, and confirm polish and symmetry are Very Good or better. View the stone or a video of it in motion: a still photograph hides exactly the faults you are looking for.

Cut matters just as much in lab-grown

A lab-grown diamond is still a diamond crystal that a human being has to cut, and it is graded on the same cut scale by the same laboratories. Because lab-grown stones cost roughly 40–60% less than natural for comparable specs, there is rarely any reason to compromise: buy an Excellent cut and put the savings into carat weight instead. See our lab-grown diamond guide, or filter our inventory by cut grade.

See it on real stones

Browse IGI-certified lab-grown diamonds by shape, carat, color, clarity and cut, at roughly 40–60% less than comparable natural stones.

Shop lab-grown diamonds Shop engagement rings

More on diamonds: The 4Cs, Color, Clarity, Carat weight, Shapes, Inclusions, Certificates, and Conflict-free.