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What do you know about
diamonds
Explore the captivating world of diamonds. Learn about their origin, beauty, and the 4 Cs that define their quality. Welcome to the world of timeless elegance and enduring brilliance.
By Fiona, founder of Ronora Diamond. Updated September 26, 2026.
Find Me Diamond shows any diamond at actual size on a finger, an ear, a neck or a wrist. A 1.00 carat round diamond measures about 6.5 mm across and covers about 38% of the width of a US size 6.5 finger. A pair of 1 carat stud earrings is 2 carats total weight, 6.5 mm per earring. A 7 inch tennis bracelet of 2 mm round diamonds holds about 74 stones, 2.16 carats in total. The same weight in another shape can measure anywhere from 5.5 mm to 10 mm, because carat is a unit of weight and not of size. Pick the jewelry, the shape and the carat weight below, and the tool draws it at true scale on your screen.
Shopping for a particular piece? See diamond stud sizes on the ear, tennis bracelet sizes on the wrist or pendant sizes on the neck.
Carat is the most misunderstood number in diamond buying. It is a weight, one fifth of a gram, and on its own it tells you nothing about how large a stone looks on a hand.
Two diamonds can weigh exactly the same and differ by more than 4 mm in length. A marquise at 1.00 ct is 10 mm long. A cushion at the same weight is 5.5 mm. Same weight, same price bracket, completely different presence on the finger.
The difference is where the weight sits. A diamond is a three dimensional object, and any weight hidden below the girdle in a deep pavilion never reaches your eye. Shapes that spread their weight across the face look larger. Shapes that carry it downward look smaller.
Choose ring, bracelet, earrings or pendant, pick a shape and set the carat weight, or the stone size in millimeters for a tennis bracelet. The diamond is drawn at true scale on a finger, a wrist, an ear or a neckline. Already have measurements and want the carat weight? Switch to millimeters. Calibrate once against a bank card and the outline matches real life on your screen.
Measure the longest axis and the widest axis of the face-up outline. Carat weight is estimated from those two figures and the proportions this shape is normally cut to.
A 1.00 ct round measures
6.50 × 6.50 mm
Drawn at true physical size once your screen is calibrated. Hold a ring up to the outline to judge it properly.
Hold any bank card against the bar below and drag the slider until the two match exactly. A standard card is 85.6 mm wide. Your setting is remembered on this device.
Same weight, twelve outlines. The bars are drawn to scale against each other, longest first.
Millimeter figures are for well proportioned stones cut to the ratio shown. Individual stones vary, so ask us for the exact measurements on any stone before you order. The Dutch Marquise is one of our own cuts and has no published trade chart; those figures are Ronora's working sizes.
Length by width in millimeters, for every shape Ronora cuts, at the proportions we cut them to. Read down your carat weight, or across your shape. The round is highlighted because it is the shape everything else gets compared against.
| Shape | 0.50 ct | 1.00 ct | 1.50 ct | 2.00 ct | 3.00 ct |
|---|---|---|---|---|---|
| Round | 5.2 × 5.2 | 6.5 × 6.5 | 7.4 × 7.4 | 8.2 × 8.2 | 9.4 × 9.4 |
| Oval | 6.1 × 4.5 | 7.7 × 5.7 | 8.8 × 6.5 | 9.7 × 7.2 | 11.1 × 8.2 |
| Princess | 4.4 × 4.4 | 5.5 × 5.5 | 6.3 × 6.3 | 6.9 × 6.9 | 7.9 × 7.9 |
| Cushion | 4.4 × 4.4 | 5.5 × 5.5 | 6.3 × 6.3 | 6.9 × 6.9 | 7.9 × 7.9 |
| Elongated Cushion | 5.0 × 3.8 | 6.2 × 4.8 | 7.1 × 5.5 | 7.9 × 6.0 | 9.0 × 6.9 |
| Radiant | 5.0 × 3.8 | 6.2 × 4.8 | 7.1 × 5.5 | 7.9 × 6.0 | 9.0 × 6.9 |
| Emerald | 5.6 × 4.0 | 7.0 × 5.0 | 8.0 × 5.7 | 8.8 × 6.3 | 10.1 × 7.2 |
| Asscher | 4.4 × 4.4 | 5.5 × 5.5 | 6.3 × 6.3 | 6.9 × 6.9 | 7.9 × 7.9 |
| Pear | 6.3 × 4.2 | 7.9 × 5.3 | 9.1 × 6.1 | 10.0 × 6.7 | 11.5 × 7.6 |
| Marquise | 7.9 × 4.0 | 10.0 × 5.0 | 11.4 × 5.7 | 12.6 × 6.3 | 14.4 × 7.2 |
| Dutch Marquise | 7.1 × 3.8 | 9.0 × 4.8 | 10.3 × 5.6 | 11.3 × 6.1 | 12.9 × 7.0 |
| Heart | 5.2 × 5.2 | 6.5 × 6.5 | 7.4 × 7.4 | 8.2 × 8.2 | 9.4 × 9.4 |
Every figure assumes a well proportioned stone at the classic ratio for that shape. Cut the same weight longer and it gets narrower; cut it rounder and it gets wider. The calculator above has a ratio control so you can see exactly what that does. For weights between these columns, remember that millimeters grow with the cube root of carat weight: doubling the weight adds about 26% to the length, not 100%.
The share of the finger's width a round diamond covers, by carat weight and US ring size. It is the stone's width divided by the inside diameter of the ring, so the smaller the finger, the bigger the same diamond looks.
| Carat | Round diameter | US size 5 (15.7 mm) | US size 6.5 (16.9 mm) | US size 8 (18.1 mm) |
|---|---|---|---|---|
| 0.50 ct | 5.2 mm | 33% | 31% | 29% |
| 0.75 ct | 5.9 mm | 38% | 35% | 33% |
| 1.00 ct | 6.5 mm | 41% | 38% | 36% |
| 1.50 ct | 7.4 mm | 47% | 44% | 41% |
| 2.00 ct | 8.2 mm | 52% | 48% | 45% |
| 2.50 ct | 8.8 mm | 56% | 52% | 49% |
| 3.00 ct | 9.4 mm | 60% | 55% | 52% |
| 4.00 ct | 10.3 mm | 66% | 61% | 57% |
| 5.00 ct | 11.1 mm | 71% | 66% | 61% |
An oval of the same weight looks more slender on the hand: a 1 carat oval is 5.7 mm across the finger, about 34% of a size 6.5 finger, and a 2 carat oval about 42%. Choose Ring in the calculator above to see any shape on your own ring size.
Stud earrings are sold by the carat weight of each earring or by the total weight of the pair. This chart gives both, with the face-up size of each earring in millimeters for the four most popular stud shapes.
| Each earring | Pair total | Round (mm) | Princess (mm) | Oval (mm) | Cushion (mm) |
|---|---|---|---|---|---|
| 0.25 ct | 0.50 ct | 4.1 × 4.1 | 3.5 × 3.5 | 4.8 × 3.6 | 3.5 × 3.5 |
| 0.50 ct | 1.00 ct | 5.2 × 5.2 | 4.4 × 4.4 | 6.1 × 4.5 | 4.4 × 4.4 |
| 0.75 ct | 1.50 ct | 5.9 × 5.9 | 5.0 × 5.0 | 7.0 × 5.2 | 5.0 × 5.0 |
| 1.00 ct | 2.00 ct | 6.5 × 6.5 | 5.5 × 5.5 | 7.7 × 5.7 | 5.5 × 5.5 |
| 1.50 ct | 3.00 ct | 7.4 × 7.4 | 6.3 × 6.3 | 8.8 × 6.5 | 6.3 × 6.3 |
| 2.00 ct | 4.00 ct | 8.2 × 8.2 | 6.9 × 6.9 | 9.7 × 7.2 | 6.9 × 6.9 |
| 2.50 ct | 5.00 ct | 8.8 × 8.8 | 7.5 × 7.5 | 10.4 × 7.7 | 7.5 × 7.5 |
| 3.00 ct | 6.00 ct | 9.4 × 9.4 | 7.9 × 7.9 | 11.1 × 8.2 | 7.9 × 7.9 |
Choose Earrings in the calculator above to see a stud in a three prong martini setting on the ear lobe, set vertically or horizontally, at actual size.
How big a solitaire pendant stone is when it hangs vertically, height by width in millimeters. The bail that holds the chain adds a few millimeters above the stone.
| Carat | Round (mm) | Oval (mm) | Pear (mm) | Emerald (mm) | Heart (mm) |
|---|---|---|---|---|---|
| 0.50 ct | 5.2 × 5.2 | 6.1 × 4.5 | 6.3 × 4.2 | 5.6 × 4.0 | 5.2 × 5.2 |
| 0.75 ct | 5.9 × 5.9 | 7.0 × 5.2 | 7.2 × 4.8 | 6.4 × 4.5 | 5.9 × 5.9 |
| 1.00 ct | 6.5 × 6.5 | 7.7 × 5.7 | 7.9 × 5.3 | 7.0 × 5.0 | 6.5 × 6.5 |
| 1.50 ct | 7.4 × 7.4 | 8.8 × 6.5 | 9.1 × 6.1 | 8.0 × 5.7 | 7.4 × 7.4 |
| 2.00 ct | 8.2 × 8.2 | 9.7 × 7.2 | 10.0 × 6.7 | 8.8 × 6.3 | 8.2 × 8.2 |
| 3.00 ct | 9.4 × 9.4 | 11.1 × 8.2 | 11.5 × 7.6 | 10.1 × 7.2 | 9.4 × 9.4 |
Choose Pendant in the calculator above to see the stone on a chain at the neckline, hung vertically or horizontally.
How many round diamonds a tennis bracelet holds, and the total carat weight, for each stone size and wrist size. The bracelet is made 0.5 in longer than the wrist so it moves comfortably, with about 0.4 mm of metal between stones.
| Stone size | 6 in wrist | 6.5 in wrist | 7 in wrist | 7.5 in wrist |
|---|---|---|---|---|
| 1.5 mm (0.012 ct each) | 86 stones, 1.06 ct | 93 stones, 1.14 ct | 100 stones, 1.23 ct | 106 stones, 1.30 ct |
| 2.0 mm (0.029 ct each) | 68 stones, 1.98 ct | 74 stones, 2.16 ct | 79 stones, 2.30 ct | 84 stones, 2.45 ct |
| 2.5 mm (0.057 ct each) | 56 stones, 3.19 ct | 61 stones, 3.47 ct | 65 stones, 3.70 ct | 70 stones, 3.98 ct |
| 3.0 mm (0.098 ct each) | 48 stones, 4.72 ct | 52 stones, 5.11 ct | 56 stones, 5.51 ct | 59 stones, 5.80 ct |
| 3.5 mm (0.156 ct each) | 42 stones, 6.56 ct | 45 stones, 7.03 ct | 48 stones, 7.49 ct | 52 stones, 8.12 ct |
| 4.0 mm (0.233 ct each) | 37 stones, 8.62 ct | 40 stones, 9.32 ct | 43 stones, 10.02 ct | 46 stones, 10.72 ct |
Counts are rounded down, and the clasp can change them by a stone or two. Choose Bracelet in the calculator above for any stone size, shape, placement (east-west, north-south or cross) and wrist size, drawn at true scale on a wrist.
A 1.00 carat round brilliant measures about 6.5 mm in diameter, a little over a quarter of an inch. That is the number to anchor everything else to, because the round is the only shape with genuinely standardized proportions.
For every other shape the answer depends on how the cutter drew it. A 1.00 ct oval is around 7.7 by 5.7 mm at the classic ratio, but the same weight stretched longer comes out nearer 8.3 by 5.5 mm. Narrower, longer, identical weight. That is why the calculator has a ratio control rather than a single fixed answer.
Measure the stone, not the setting. Take the longest axis first, then the widest axis at ninety degrees to it, both in millimeters. Those two figures are all the calculator needs to work back to an approximate carat weight.
If the diamond is already set, prongs and a bezel add width and a caliper reading will run large. A grading report is always the better source: it lists the measurements to two decimal places alongside the weight. Our diamond anatomy guide explains how to read the rest of that report.
Three things decide how large a diamond looks, and only one of them is the carat weight.
The table below ranks all twelve shapes by how long they actually measure at one carat, so you can see the spread rather than guess at it.
All twelve shapes at 1.00 ct, ranked by how long they actually measure. Every stone in this table weighs exactly the same. The only thing changing is where the cutter put that weight.
| Shape | Length at 1.00 ct | Against a 1 ct round | What that means on the hand |
|---|---|---|---|
| Marquise | 10.0 mm | 54% longer | The longest outline at any weight, and the most finger-lengthening shape there is |
| Dutch Marquise | 9.0 mm | 38% longer | Nearly as long as a marquise, built from six straight sides instead of curves |
| Pear | 8.0 mm | 22% longer | Long, but one rounded end makes it read softer than a marquise |
| Oval | 7.7 mm | 18% longer | The best all-rounder: longer than a round and covers slightly more area too |
| Emerald | 7.0 mm | 8% longer | A wide open table makes it look larger than its length alone suggests |
| Round | 6.5 mm | the benchmark | The reference every other shape on this page is measured against |
| Heart | 6.5 mm | same length | As long as a round, and noticeably wider across the shoulders |
| Radiant | 6.2 mm | 4% shorter | Slightly shorter than a round, and a touch narrower with it |
| Elongated Cushion | 6.2 mm | 4% shorter | Reads longer than a square cushion without giving up the soft corners |
| Princess | 5.5 mm | 15% shorter | Square corners fill the whole outline, so it looks bigger than its length |
| Asscher | 5.5 mm | 15% shorter | Compact, and the stepped corners take a little off each side |
| Cushion | 5.5 mm | 15% shorter | The shortest of the twelve, because it carries more of its weight in depth |
Length is not the whole story. An emerald cut is only 8% longer than a round but its wide flat table makes it read larger again, while a marquise is 54% longer and yet covers roughly the same face-up area. If maximum presence per carat is the goal, the elongated shapes win. If you want the most light back, the round is still unbeaten. Compare all twelve in the diamond shapes guide.
The same stone reads differently on different hands. On a size 4 finger a 1.00 ct round covers a much larger share of the width than it does on a size 9, so it looks bigger without being bigger.
The practical rule: on smaller fingers a long elongated shape can start to look oversized, and a round, cushion or asscher sits more comfortably. On longer fingers the elongated shapes are where the drama is, and a small round can disappear. This is a question of proportion rather than size, and it is worth settling before you fix on a carat weight.
No, and chasing millimeters can cost you both size and brightness at once.
A stone cut too shallow measures wide for its weight but leaks light out of the bottom, which reads as a dull or watery center rather than a bigger diamond. That is why every Ronora stone is Excellent cut only. Within Excellent proportions there is still a genuine spread difference between shapes, and that difference is what the tables on this page show. Outside them, every extra millimeter is bought with sparkle.
Twice the weight, but only about a quarter longer. A 1.00 ct round is 6.5 mm across and a 2.00 ct round is 8.2 mm, an increase of roughly 26%.
That is not a quirk of the round: it holds for every shape, because weight is a volume and every dimension grows with the cube root of it. Doubling the carat weight always adds about 26% to the length. Tripling it adds about 44%. This is the single most useful thing to know when you are weighing a jump in carat weight against the price of it, because the price rises far faster than the millimeters do.
The honest advice is to shop in millimeters rather than carats. Decide how much finger you want the diamond to cover, read the size off the chart above, and let the carat weight fall where it falls. Every Ronora diamond is a real CVD lab grown diamond, Excellent cut, in the D-E-F colorless range, cut to order in Surat. If you want a particular length or a particular ratio, send us the millimeters and we will cut to them. Start with the diamond shapes guide if you have not settled on an outline yet, or the carat weight guide for what the weight itself actually means.
A 1 carat round diamond measures about 6.5 mm across, a little over a quarter of an inch. The same weight measures about 7.7 × 5.7 mm as an oval, 5.5 × 5.5 mm as a princess and 10.0 × 5.0 mm as a marquise, because carat is a weight and not a size.
A 2 carat round diamond is about 8.2 mm across. On a US size 6.5 finger, which is 16.9 mm across, it covers about 48% of the finger's width, against 38% for a 1 carat round.
A 3 carat round is about 9.4 mm across and covers about 55% of the width of a US size 6.5 finger. A 3 carat oval is about 11.1 × 8.2 mm and runs further along the finger.
Not usually, but it looks bigger. On a US size 4 finger, 14.9 mm across, a 1 carat round covers about 44% of the width, compared with 38% on a size 7. On a small hand, a round, cushion or Asscher sits more compactly than a long marquise.
There is no single right answer, so compare them at actual size. On a US size 7 finger, 17.3 mm across, a 1 carat round covers about 38% of the width, a 1.5 carat about 43% and a 2 carat about 47%.
Stud sizes are quoted per earring or as a pair total. A 0.25 carat round stud is about 4.1 mm across, a 0.5 carat about 5.2 mm and a 1 carat about 6.5 mm. A pair of 1 carat studs is 2 carats total weight.
A 1 carat round stud measures about 6.5 mm across, and a 1 carat princess stud about 5.5 mm square. Choose Earrings in Find Me Diamond to see it on an ear lobe at actual size.
It depends on the stone size and the bracelet length. A 7 inch bracelet, the usual length for a 6.5 inch wrist, holds about 93 stones of 1.5 mm (1.14 ct), 74 stones of 2 mm (2.16 ct), 52 stones of 3 mm (5.11 ct) or 40 stones of 4 mm (9.32 ct), allowing about 0.4 mm of metal between stones.
Measure your wrist just below the wrist bone and add half an inch. A 6.5 inch wrist wears a 7 inch tennis bracelet, and a 7 inch wrist wears 7.5 inches.
A 1 carat round pendant stone is about 6.5 mm across and a 2 carat about 8.2 mm, with the bail above it. A 1 carat pear hung point up is about 7.9 × 5.3 mm.
Yes. A lab grown diamond is the same material as a mined diamond, with the same density, so the same carat weight and cut give the same size. Every Ronora diamond is a real CVD lab grown diamond.
At the same carat weight the marquise measures longest: a 1 carat marquise is about 10.0 mm long, against 6.5 mm for a round. Pear, oval and emerald also measure longer than a round, while princess, cushion and Asscher measure 5.5 mm across.
Very close on most screens. For exact size, hold a bank card, which is 85.6 mm wide, against the calibration bar and adjust it until the two match; the setting is saved on that device. Sizes are for well proportioned stones at the classic ratio for each shape, so ask us for the exact measurements of a specific stone before you order.
Find Me Diamond is free to use on your own blog or website. Paste these two lines where you want it to appear, and keep the credit link to Ronora Diamond.
<div data-find-me-diamond></div>
<script src="https://ronoradiamond.com/cdn/shop/files/find-me-diamond-embed.js" async></script>
To open it on a particular piece, add data-jewelry="ring", "earring", "pendant" or "bracelet", and optionally data-shape="oval" and data-carat="1", to the first line. For questions or a partner version, contact us.
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