Kove Jewelry
How big is a 1, 1.5, 2, 2.5 or 3 carat diamond?
Most carat size charts online are the same chart, copied from site to site, with one ideal number per weight. Real stones are not ideal. So we measured: the table below gives the median size in millimetres of certified lab-grown diamonds available through our partner supplier network, for nine shapes and five weights, sampled on 17 October 2026.
Why carat is not size
Carat is a unit of weight: one metric carat is 200 milligrams, divided into 100 points. GIA puts it plainly — carat measures weight, not size.
What you see on a hand is the face-up spread: the outline of the stone from above. Two stones of the same weight can spread differently, because part of the weight sits below the girdle, in the depth of the stone. A deeper cut hides more of its weight underneath; a shallower one spreads it wider but can lose brightness. That is why the numbers below are medians, not promises — every individual stone varies around them, and its IGI or GIA report lists its exact measurements.
The chart: size in millimetres by shape and carat
Length × width in millimetres (for round, the two diameters). Median of certified white lab-grown stones available through our partner supplier network, sampled 17 October 2026.
| Shape | 1 ct | 1.5 ct | 2 ct | 2.5 ct | 3 ct |
|---|---|---|---|---|---|
| Round | 6.48 × 6.44 | 7.41 × 7.37 | 8.15 × 8.11 | 8.79 × 8.74 | 9.33 × 9.28 |
| Oval | 8.14 × 5.66 | 9.29 × 6.48 | 10.20 × 7.12 | 11.01 × 7.63 | 11.72 × 8.13 |
| Pear | 8.90 × 5.58 | 10.19 × 6.41 | 11.25 × 7.08 | 12.13 × 7.59 | 12.85 × 8.07 |
| Marquise | 10.35 × 5.26 | 11.84 × 6.00 | 12.93 × 6.59 | 14.07 × 7.09 | 14.84 × 7.52 |
| Emerald | 6.88 × 4.74 | 7.84 × 5.41 | 8.56 × 5.94 | 9.26 × 6.41 | 9.80 × 6.79 |
| Radiant | 7.13 × 4.97 | 8.12 × 5.68 | 8.92 × 6.24 | 9.57 × 6.69 | 10.27 × 7.16 |
| Princess | 5.50 × 5.44 | 6.29 × 6.22 | 6.93 × 6.84 | 7.46 × 7.36 | 7.93 × 7.84 |
| Asscher | 5.60 × 5.53 | 6.38 × 6.33 | 7.01 × 6.96 | 7.55 × 7.44 | 8.04 × 7.92 |
| Heart | 6.99 × 6.22 | 7.99 × 7.15 | 8.78 × 7.83 | 9.46 × 8.36 | 10.00 × 8.96 |
How we measured: a random 8% sample of the white (colourless to near-colourless, not fancy-coloured) lab-grown stones in the live partner feed that powers our stone picker, queried 17 October 2026 — 16,513 stones in total. Weight bands: 0.98–1.04, 1.48–1.55, 1.98–2.06, 2.48–2.56 and 2.98–3.08 ct. Stones per shape: round 7,475 · oval 1,967 · emerald 1,570 · pear 1,370 · radiant 1,173 · princess 1,044 · marquise 938 · heart 660 · asscher 316. The smallest single cell is asscher 2.5 ct with 38 stones; cushion was left out because its sample was too small. Princess and asscher are measured side to side — corner to corner they are longer.
What doubling the carat really does
Weight grows with volume, and volume grows with the cube of the size. So when the weight doubles, the diameter grows far less. In our data a round goes from 6.48 mm at 1 carat to 8.15 mm at 2 carats — about 26% wider, not twice as wide.
The surface you see from above grows faster than the diameter: a 2 carat round shows roughly 58% more face-up area than a 1 carat, and a 3 carat round (9.33 mm) roughly twice the face-up area of a 1 carat. Put differently: to see a stone that looks about twice as big from above, you go from 1 carat to about 3, not to 2.
- Round 1 → 1.5 ct: 6.48 → 7.41 mm (+14%)
- Round 1 → 2 ct: 6.48 → 8.15 mm (+26%)
- Round 1 → 3 ct: 6.48 → 9.33 mm (+44%)
Elongated shapes look bigger for their carat
Long shapes spread more of their weight along the finger. Compare the longest side of each shape at 1 carat with the 6.48 mm of a 1 carat round:
- Marquise: 10.35 mm long — about 60% longer than a round is wide.
- Pear: 8.90 mm — about 37% longer.
- Oval: 8.14 mm — about 26% longer; the same as the 8.15 mm diameter of a 2 carat round.
- Radiant 7.13 mm and emerald 6.88 mm — slightly longer, but narrower (under 5 mm).
- Princess 5.50 mm and asscher 5.60 mm side to side — square shapes carry more weight in their depth and corners, so they measure smaller across than a round of the same weight.
Length is not everything: an elongated stone is also narrower. A 1 carat oval is 5.66 mm wide against 6.44 mm for a round. On the hand it reads as bigger mainly because the eye follows the long side.
How it looks on a hand
Millimetres on a screen are hard to picture. The easiest way to judge a size is to see it on a hand.
In our Solitaire Studio you move a slider from 1 to 5 carats and see the stone on a real-hand reference photo, in the shape and gold colour you choose.
How to choose: budget, size and her hand
- Decide what matters more: the weight on the report or the size on the hand. If it is the look, an oval, pear or marquise gives you more length per carat than a round.
- Price does not rise in a straight line with carat — it jumps at round weights such as 1, 1.5 and 2 carats. GIA notes that a 0.99 ct and a 1.00 ct stone are hard to tell apart by eye. For how price per carat changes by weight band, see lab-grown diamond prices in 2026.
- Size is only one of the 4Cs. A well-cut stone of slightly lower weight often looks livelier than a bigger, poorly cut one. The 4Cs explained.
- General advice, not a rule: the same stone looks larger on a slim finger than on a broader one, and elongated shapes tend to make a finger look longer. Think also about her day — a tall, wide stone catches more on gloves, bags and knitwear.
No need to measure anything at home
You do not need to print rulers or cut paper circles for the stone. Every centre stone above 0.30 ct in a Kove ring comes with an IGI or GIA report, and the report gives its exact measurements in millimetres. The one thing worth measuring is her ring size:
Questions people ask
How big is a 1 carat diamond in mm?
A 1 carat round diamond is typically about 6.5 mm across — the median in our October 2026 sample of certified lab-grown stones was 6.48 × 6.44 mm. A 1 carat oval is about 8.1 × 5.7 mm, a pear about 8.9 × 5.6 mm, an emerald cut about 6.9 × 4.7 mm and a princess about 5.5 mm side to side.
How big is a 2 carat oval?
About 10.2 × 7.1 mm. The median 2 carat oval in our October 2026 sample measured 10.20 × 7.12 mm. Individual stones vary around that; the stone’s IGI or GIA report gives its exact measurements.
Does a 2 carat diamond look twice as big as 1 carat?
No. Doubling the weight makes a round about 26% wider (6.48 → 8.15 mm in our data) and gives roughly 58% more face-up area. A stone that looks about twice as big from above is closer to 3 carats (9.33 mm).
Which shape looks biggest for its carat?
Marquise, then pear, then oval. At 1 carat a marquise is about 10.4 mm long, a pear about 8.9 mm and an oval about 8.1 mm, against about 6.5 mm for a round. Square shapes such as princess and asscher measure smaller across than a round of the same weight.
What carat size should I choose for an engagement ring?
There is no reliable public figure for a "most popular" size that we could verify, so decide from three things: the budget you are comfortable with, how the stone looks on her hand, and the shape — an elongated shape gives more visible size per carat. Our Solitaire Studio shows 1 to 5 carats on a real-hand photo so you can compare.
Is a lab-grown 1 carat the same size as a natural 1 carat?
Yes, for the same shape and cut proportions. According to GIA, lab-grown diamonds have essentially the same chemical composition, crystal structure and physical properties as natural diamonds — so the same weight takes up the same volume. Differences in size between two individual stones come from how each is cut, not from its origin.
Sources
Millimetre sizes: Kove first-party data — median of certified lab-grown stones available through our partner supplier network, sampled 17 October 2026.
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