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Diamond Depth Percentage by Shape: Ideal Ranges Explained
Diamond depth percentage is the stone's height (culet to table) divided by its average width, and it is one of the two proportions — alongside table percentage — that decide whether light bounces back to your eye or leaks out the sides and bottom. The ideal range depends on the shape: a round brilliant wants roughly 59–62.5% depth, while an emerald cut needs 61–67% to look right. Cut too shallow and a diamond looks glassy and washed out; cut too deep and it looks dark and smaller than its carat weight suggests. The grade-by-grade comparison lives in Very Good vs Excellent cut grades.
Key takeaways
- Depth % = total height ÷ average width, expressed as a percentage — it is different from table %, which measures only the flat top facet.
- Ideal depth ranges are shape-specific. There is no single number that works for round, oval, cushion, and emerald cuts alike.
- Too shallow leaks light out the pavilion; too deep traps light and can create a visible dark "nail head" or bow-tie effect.
- Depth and table percentage work together — a diamond can have a good table and a poor depth, or vice versa, and still underperform.
- Certificates (IGI, GIA) print exact depth % — always check it against the shape-specific ideal range, not a generic "59–62%" rule of thumb.
- Every Montare diamond is cut to ideal table and depth for its specific shape, not just an average industry range.
What is diamond depth percentage, exactly?
Depth percentage measures how tall a diamond is relative to how wide it is. You calculate it by dividing the diamond's total depth (in millimetres, measured from the table down to the culet) by its average girdle diameter, then multiplying by 100. A round diamond that is 6.50mm wide and 4.03mm deep has a depth percentage of 62% (4.03 ÷ 6.50 × 100).
Every diamond certificate — IGI or GIA — prints this number, usually right next to table percentage. On its own, a depth percentage tells you almost nothing. You need to compare it against the ideal range for that specific shape, because a proportion that reads as excellent on a round brilliant can read as poorly cut on an emerald or radiant.
Depth percentage vs. table percentage: what's the difference?
These two numbers get confused constantly because they appear side by side on every certificate, but they measure different things:
- Table percentage is the width of the flat top facet (the table) divided by the diamond's total width. It controls how large and bright the face-up "window" into the stone looks.
- Depth percentage is the diamond's total height divided by its width. It controls how far light has to travel inside the stone before it either bounces back to your eye or escapes out the bottom.
They interact. A diamond can have a textbook table percentage and still look dull if the depth is wrong, because depth determines the angles at which light hits the pavilion facets and reflects — or doesn't. This is why Montare's standard specifies both together rather than either in isolation. For the mechanics of table percentage specifically, see our companion guide, Diamond Table Percentage by Shape.
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Design your ringWhy depth percentage matters more than most buyers realize
Depth is the single biggest lever on whether a diamond looks alive or lifeless, for one simple reason: it is the primary control on the angles of the pavilion facets, and those angles decide whether light undergoes total internal reflection (bouncing back up through the crown to your eye) or simply exits out the side or bottom of the stone unseen.
Cut too shallow
A shallow diamond has pavilion facets angled too close to flat. Light entering the crown hits the pavilion at an angle that lets it escape straight through the bottom instead of reflecting. The visual result is a diamond that looks watery and washed out, with a dark or grey ring visible through the table — sometimes called a "fish eye" effect. Shallow stones also face up larger for their carat weight, which is part of why buyers should never chase a bigger-looking diamond without checking the proportions behind it.
Cut too deep
A deep diamond has pavilion facets angled too steeply. Light bounces around inside the stone more times than it should and a portion escapes out the sides of the pavilion rather than back through the crown. The visual result is a diamond with a dark centre — often called a "nail head" on round brilliants — that looks smaller and heavier than its carat weight implies, because so much of that extra weight is hidden below the girdle where it adds no visible size.
The ideal middle
Within the ideal range, light entering the crown reflects internally off the pavilion facets at the correct angles and exits back through the table and crown facets toward the viewer's eye. This is what produces the bright, lively brilliance and contrast pattern that makes a well-cut diamond look different from a poorly cut one of the same carat weight, colour, and clarity.
Ideal depth percentage by shape
Depth percentage ranges shift meaningfully by shape, because each shape's facet geometry changes how light travels through the stone. The table below shows Montare's house standard — every shape is cut to sit inside its own ideal range, not a generic industry average.
| Shape | Ideal table % | Ideal depth % | Typical L:W ratio |
|---|---|---|---|
| Round brilliant | 54–57% | 59–62.5% | 1.00 (perfectly round) |
| Oval | 54–58% | 58–62% | 1.35–1.50 |
| Cushion (elongated) | 60–62% | 61–67% | 1.25–1.35 |
| Emerald | 62–66% | 61–67% | 1.30–1.50 |
| Radiant | 62–66% | 61–67% | 1.20–1.35 |
| Pear | 54–58% | 58–62% | 1.45–1.70 |
| Marquise | 54–58% | 58–62% | 1.85–2.10 |
Notice that step and fancy-brilliant shapes like emerald and radiant carry a wider, deeper ideal band than round or oval. That is not a lower standard — it reflects how those facet patterns actually perform. Emerald cuts use large, open step facets instead of the round brilliant's many small triangular ones, so they need more depth to generate the same light return, and they show clarity more openly as a trade-off (see our guide to diamond clarity, from VVS to SI, for how that affects grade choice).
Montare's cushion cuts are elongated (roughly 1.25–1.35 length-to-width) rather than square — a deliberate house choice, since a square cushion's proportions behave differently and are not part of our lineup.
How to check depth percentage on your own certificate
If you already have a diamond, or are comparing certificates while shopping:
- Find the "Depth %" or "Total Depth" field on the IGI or GIA report — it's listed with table % near the top of the proportions section.
- Identify the shape, then compare against the ideal range for that shape (use the table above, not a generic 59–62% round-brilliant rule).
- Check depth and table together. A diamond can pass on one and fail on the other — both need to sit inside range for the stone to perform as intended.
- Cross-reference against the cut grade if one is issued. IGI grades cut (Excellent to Poor) for both round and most fancy shapes; GIA only issues a cut grade on round brilliants. See IGI vs. GIA for lab-grown diamonds for what each certificate actually covers.
- Remember polish and symmetry are separate grades again — a diamond can have ideal proportions and still lose brilliance to poor symmetry. Our guide to diamond symmetry and polish grades covers that layer.
Every Montare diamond is Triple Excellent — Excellent cut, polish, and symmetry — and is cut to the ideal table and depth percentage for its own shape, not a generic average. Paired with D–E colour, VVS1–VVS2 clarity, a 3 carat minimum, and IGI certification on every stone, it's the tightest combination of proportions and clarity we could set as a floor. Bespoke design and a lifetime setting-upgrade promise come standard. Read the full breakdown on our standards page.
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Open the ring builder →Frequently asked questions
What is a good depth percentage for a diamond?
It depends entirely on the shape. For a round brilliant, 59–62.5% is the ideal range. For an emerald or radiant cut, 61–67% is ideal because those shapes need more depth to perform well. There is no single "good" number that applies across every shape.
Is a lower or higher depth percentage better?
Neither — the goal is the ideal range for that shape, not the lowest or highest number available. Too low (shallow) leaks light out the bottom; too high (deep) traps light and darkens the centre. Both extremes reduce brilliance.
Does depth percentage affect how big a diamond looks?
Yes. A shallow diamond spreads more of its weight across its face-up width, so it can look larger for its carat weight — but usually at the cost of brilliance. A deep diamond hides weight below the girdle where it adds no visible size. The ideal range balances size and sparkle rather than maximizing one at the other's expense.
Do lab-grown diamonds have different ideal depth ranges than mined diamonds?
No. Lab-grown diamonds are chemically, physically, and optically identical to mined diamonds, so the same physics of light refraction and the same ideal proportion ranges apply to both. A lab-grown diamond cut to ideal table and depth performs exactly as brilliantly as a mined diamond cut to the same proportions.
Where do I find the depth percentage on my diamond's certificate?
It's printed on the IGI or GIA certification report, typically in the "Proportions" section alongside table percentage, girdle thickness, and culet size. If you're shopping and a listing doesn't show it, ask for the certificate directly before buying.
Why do emerald and radiant cuts have a wider depth range than round diamonds?
Their step-cut and mixed-cut facet patterns are geometrically different from a round brilliant's. Larger, more open facets need more depth to bend and return light effectively, so their ideal window sits deeper and wider (61–67%) than a round brilliant's tighter 59–62.5% band.
The Montare standard
Lab-grown · D–E colour · VVS clarity · Triple Excellent · 3ct minimum · IGI certified
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