Diamond Size Chart — Millimetres to Carat
Updated 27 September 2026
Convert a millimetre measurement into a carat weight, or a carat weight into the size it actually is on the hand, for every diamond shape we sell. Backed by industry-direct supplier measurements and 630,306 certified stones.
Two things make a chart like this worth trusting. The first is where the figures come from: ours are measured, not transcribed from another retailer. The second is context: face-up size varies with ratio, depth, girdle thickness and other proportions. Every figure here publishes the ratio beside it — a 2 carat oval is a very different stone at 1.30 than at 1.50.
Diamond size converter
Pick a shape, then enter either a measurement or a weight. The converter answers from the same figures as the tables below and tells you which of them the answer rests on.
Measure across the top of the stone, not through the setting.
Diamond carat to millimetre chart
How big each weight actually is, shape by shape. Read across a row to see how a single weight changes size as the shape changes, and down a column to compare shapes at a weight you have in mind. The elongated shapes face up larger per carat, which is most of why they have taken over the market.
| Shape | Ratio | 0.30 ct | 0.50 ct | 1.00 ct | 1.50 ct | 2.00 ct | 3.00 ct |
|---|---|---|---|---|---|---|---|
| Round brilliant | 1.00 | 4.3 mm | 5.1 mm | 6.4 mm | 7.3 mm | 8.1 mm | 9.2 mm |
| Princess | 1.00 | 3.7 mm | 4.4 mm | 5.5 mm | 6.3 mm | 6.9 mm | 7.9 mm |
| Asscher | 1.00 | 3.8 mm | 4.4 mm | 5.5 mm | 6.3 mm | 6.9 mm | 8.0 mm |
| Cushion (square) | 1.00 | 3.8 mm | 4.6 mm | 5.7 mm | 6.6 mm | 7.2 mm | 8.3 mm |
| Cushion (elongated) | 1.30 | 4.5 × 3.4 mm | 5.3 × 4.1 mm | 6.6 × 5.1 mm | 7.6 × 5.9 mm | 8.5 × 6.5 mm | 9.8 × 7.5 mm |
| Emerald | 1.40 | 4.5 × 3.2 mm | 5.3 × 3.8 mm | 6.6 × 4.7 mm | 7.6 × 5.4 mm | 8.4 × 6.0 mm | 9.6 × 6.8 mm |
| Radiant | 1.40 | 4.7 × 3.4 mm | 5.5 × 4.0 mm | 7.0 × 5.0 mm | 8.0 × 5.7 mm | 8.8 × 6.3 mm | 10.1 × 7.1 mm |
| Oval | 1.40 | 5.3 × 3.8 mm | 6.3 × 4.5 mm | 7.9 × 5.6 mm | 9.1 × 6.5 mm | 9.9 × 7.1 mm | 11.4 × 8.1 mm |
| Pear | 1.55 | 5.8 × 3.7 mm | 6.9 × 4.4 mm | 8.6 × 5.5 mm | 9.9 × 6.4 mm | 10.9 × 7.0 mm | 12.4 × 8.0 mm |
| Marquise | 1.90 | 6.7 × 3.5 mm | 7.9 × 4.2 mm | 10.0 × 5.2 mm | 11.4 × 6.0 mm | 12.7 × 6.6 mm | 14.4 × 7.5 mm |
| Heart | 0.90 | 4.1 × 4.6 mm | 4.9 × 5.5 mm | 6.1 × 6.9 mm | 7.0 × 7.9 mm | 7.7 × 8.7 mm | 8.8 × 9.9 mm |
Each figure is the median of our own GIA and IGI certified stones at that exact weight and ratio, from a sample of 630,306 stones. Snapshot 2026-08-30. Cut proportion moves these figures — a stone cut deep carries weight below the setting line where the eye never sees it, so always read the certificate's own measurements line.
Millimetre to carat, shape by shape
Length and width give an indicative weight range, not an exact carat weight. Depth, girdle thickness and other proportions also affect weight. Use the individual grading report or a measured loose-stone weight for an exact figure. Rounds start at 1 mm because that is where melee starts; the fancy shapes start at 2 mm, below which they are not cut commercially.
Round brilliant diamond size chart
| Diameter | Carat weight | Typical range | Based on |
|---|---|---|---|
| 1.0 mm | 0.005 ct | — | Supplier measurement |
| 1.1 mm | 0.006 ct | — | Supplier measurement |
| 1.2 mm | 0.008 ct | — | Supplier measurement |
| 1.3 mm | 0.01 ct | — | Supplier measurement |
| 1.4 mm | 0.012 ct | — | Supplier measurement |
| 1.5 mm | 0.015 ct | — | Supplier measurement |
| 1.6 mm | 0.017 ct | — | Supplier measurement |
| 1.7 mm | 0.02 ct | — | Supplier measurement |
| 1.8 mm | 0.023 ct | — | Supplier measurement |
| 1.9 mm | 0.027 ct | — | Supplier measurement |
| 2.0 mm | 0.03 ct | — | Supplier measurement |
| 2.1 mm | 0.04 ct | — | Supplier measurement |
| 2.2 mm | 0.045 ct | — | Supplier measurement |
| 2.3 mm | 0.05 ct | — | Supplier measurement |
| 2.4 mm | 0.055 ct | — | Supplier measurement |
| 2.5 mm | 0.06 ct | — | Supplier measurement |
| 2.6 mm | 0.07 ct | — | Supplier measurement |
| 2.7 mm | 0.08 ct | — | Supplier measurement |
| 2.8 mm | 0.085 ct | 0.08–0.09 ct | Supplier measurement |
| 2.9 mm | 0.095 ct | 0.09–0.10 ct | Supplier measurement |
| 3.0 mm | 0.10 ct | 0.10–0.11 ct | Supplier measurement |
| 3.1 mm | 0.12 ct | 0.11–0.12 ct | Supplier measurement |
| 3.2 mm | 0.13 ct | 0.12–0.13 ct | Supplier measurement |
| 3.3 mm | 0.14 ct | 0.14–0.15 ct | Supplier measurement |
| 3.4 mm | 0.15 ct | 0.15–0.16 ct | Supplier measurement |
| 3.5 mm | 0.17 ct | 0.16–0.17 ct | Supplier measurement |
| 3.6 mm | 0.17 ct | 0.17–0.18 ct | Supplier measurement |
| 3.7 mm | 0.20 ct | 0.19–0.21 ct | Supplier measurement |
| 3.8 mm | 0.22 ct | 0.21–0.23 ct | Supplier measurement |
| 3.9 mm | 0.23 ct | 0.23–0.24 ct | Supplier measurement |
| 4.0 mm | 0.25 ct | 0.24–0.26 ct | Supplier measurement |
| 4.1 mm | 0.28 ct | 0.26–0.29 ct | Supplier measurement |
| 4.2 mm | 0.30 ct | — | 643 stones |
| 4.4 mm | 0.32 ct | 0.30–0.33 ct | 6,017 stones |
| 4.5 mm | 0.34 ct | 0.33–0.36 ct | 4,389 stones |
| 4.6 mm | 0.37 ct | 0.35–0.39 ct | 4,151 stones |
| 4.7 mm | 0.40 ct | 0.38–0.40 ct | 5,494 stones |
| 4.8 mm | 0.41 ct | 0.40–0.43 ct | 4,068 stones |
| 4.9 mm | 0.44 ct | 0.43–0.46 ct | 3,817 stones |
| 5.0 mm | 0.50 ct | 0.47–0.54 ct | 16,095 stones |
| 5.5 mm | 0.63 ct | 0.56–0.70 ct | 19,039 stones |
| 5.8 mm | 0.74 ct | 0.70–0.80 ct | 277 stones |
| 6.0 mm | 0.82 ct | 0.73–0.92 ct | 10,071 stones |
| 6.4 mm | 1.01 ct | 1.00–1.03 ct | 865 stones |
| 6.5 mm | 1.04 ct | 1.00–1.10 ct | 74,250 stones |
| 6.9 mm | 1.25 ct | 1.20–1.30 ct | 247 stones |
| 7.0 mm | 1.31 ct | 1.20–1.47 ct | 18,755 stones |
| 7.3 mm | 1.50 ct | 1.47–1.53 ct | 530 stones |
| 7.5 mm | 1.54 ct | 1.50–1.60 ct | 49,339 stones |
| 8.0 mm | 2.04 ct | 1.90–2.12 ct | 47,607 stones |
| 8.7 mm | 2.50 ct | 2.42–2.58 ct | 332 stones |
| 9.0 mm | 2.64 ct | 2.47–3.09 ct | 38,537 stones |
| 9.2 mm | 3.01 ct | 2.86–3.04 ct | 271 stones |
| 10.0 mm | 3.74 ct | 3.42–4.10 ct | 15,252 stones |
| 10.2 mm | 4.05 ct | 3.93–4.10 ct | 79 stones |
| 11.0 mm | 5.01 ct | 4.52–5.52 ct | 8,869 stones |
| 12.0 mm | 6.08 ct | 6.00–7.06 ct | 2,913 stones |
| 13.0 mm | 8.05 ct | 7.61–9.03 ct | 1,129 stones |
| 14.0 mm | 10.04 ct | 9.05–11.04 ct | 720 stones |
| 15.0 mm | 12.10 ct | 11.47–13.32 ct | 147 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book — the sizes and weights the trade actually deals in. Covers 1.0 mm to 15.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our round brilliant buying guide.
Princess diamond size chart
| Diameter | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 mm | 0.05 ct | — | Supplier measurement |
| 2.1 mm | 0.06 ct | — | Supplier measurement |
| 2.2 mm | 0.07 ct | — | Supplier measurement |
| 2.3 mm | 0.08 ct | — | Supplier measurement |
| 2.4 mm | 0.09 ct | — | Supplier measurement |
| 2.5 mm | 0.10 ct | — | Supplier measurement |
| 2.6 mm | 0.11 ct | — | Supplier measurement |
| 2.7 mm | 0.12 ct | — | Supplier measurement |
| 2.8 mm | 0.13 ct | — | Supplier measurement |
| 3.0 mm | 0.15 ct | 0.14–0.17 ct | Supplier measurement |
| 3.2 mm | 0.20 ct | 0.18–0.23 ct | Supplier measurement |
| 3.5 mm | 0.26 ct | 0.23–0.29 ct | Supplier measurement |
| 3.7 mm | 0.31 ct | 0.30–0.32 ct | 313 stones |
| 3.9 mm | 0.36 ct | 0.33–0.38 ct | 237 stones |
| 4.1 mm | 0.41 ct | 0.39–0.45 ct | 187 stones |
| 4.3 mm | 0.49 ct | 0.45–0.52 ct | 202 stones |
| 4.5 mm | 0.55 ct | 0.51–0.59 ct | 371 stones |
| 4.7 mm | 0.64 ct | 0.58–0.70 ct | 236 stones |
| 5.0 mm | 0.80 ct | 0.70–0.90 ct | 939 stones |
| 5.5 mm | 1.04 ct | 0.95–1.10 ct | 5,977 stones |
| 6.0 mm | 1.34 ct | 1.12–1.53 ct | 2,519 stones |
| 6.3 mm | 1.53 ct | 1.50–1.59 ct | 110 stones |
| 6.5 mm | 1.58 ct | 1.51–1.81 ct | 5,051 stones |
| 6.9 mm | 2.01 ct | 1.91–2.07 ct | 90 stones |
| 7.0 mm | 2.06 ct | 1.94–2.11 ct | 7,737 stones |
| 7.4 mm | 2.50 ct | 2.37–2.78 ct | 147 stones |
| 8.0 mm | 3.07 ct | 2.94–3.53 ct | 4,052 stones |
| 9.0 mm | 4.17 ct | 4.00–5.07 ct | 3,101 stones |
| 10.0 mm | 5.57 ct | 5.04–6.93 ct | 708 stones |
| 11.0 mm | 7.79 ct | 7.04–9.05 ct | 204 stones |
| 12.0 mm | 10.06 ct | 9.17–10.76 ct | 105 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book — the sizes and weights the trade actually deals in. Covers 2.0 mm to 12.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our princess buying guide.
Asscher diamond size chart
| Diameter | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 mm | 0.047 ct | — | Calculated |
| 2.5 mm | 0.093 ct | — | Calculated |
| 3.0 mm | 0.16 ct | — | Calculated |
| 3.5 mm | 0.25 ct | — | Calculated |
| 3.8 mm | 0.31 ct | 0.30–0.33 ct | 80 stones |
| 4.4 mm | 0.50 ct | 0.50–0.52 ct | 86 stones |
| 4.9 mm | 0.71 ct | 0.70–0.73 ct | 112 stones |
| 5.0 mm | 0.80 ct | 0.72–0.90 ct | 278 stones |
| 5.5 mm | 1.02 ct | 0.95–1.08 ct | 2,163 stones |
| 6.0 mm | 1.30 ct | 1.10–1.50 ct | 959 stones |
| 6.3 mm | 1.51 ct | 1.50–1.55 ct | 203 stones |
| 6.5 mm | 1.55 ct | 1.50–1.73 ct | 1,843 stones |
| 6.9 mm | 2.00 ct | 1.97–2.10 ct | 119 stones |
| 7.0 mm | 2.04 ct | 1.97–2.10 ct | 1,967 stones |
| 7.5 mm | 2.53 ct | 2.26–2.64 ct | 604 stones |
| 8.0 mm | 3.04 ct | 2.89–3.42 ct | 969 stones |
| 9.0 mm | 4.09 ct | 3.91–5.04 ct | 792 stones |
| 10.0 mm | 5.26 ct | 5.02–6.33 ct | 305 stones |
| 11.0 mm | 8.01 ct | 7.05–8.93 ct | 94 stones |
| 12.0 mm | 10.07 ct | 9.36–11.02 ct | 92 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book where it carries the shape, and are calculated from the trade weight formula where it does not. Covers 2.0 mm to 12.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our asscher buying guide.
Cushion (square) diamond size chart
| Diameter | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 mm | 0.041 ct | — | Calculated |
| 2.5 mm | 0.081 ct | — | Calculated |
| 3.0 mm | 0.14 ct | — | Calculated |
| 3.5 mm | 0.22 ct | — | Calculated |
| 3.8 mm | 0.30 ct | 0.30–0.31 ct | 69 stones |
| 4.6 mm | 0.51 ct | 0.47–0.58 ct | 72 stones |
| 5.0 mm | 0.72 ct | 0.66–0.81 ct | 297 stones |
| 5.5 mm | 1.01 ct | 0.81–1.07 ct | 1,436 stones |
| 6.0 mm | 1.06 ct | 1.00–1.28 ct | 2,184 stones |
| 6.5 mm | 1.52 ct | 1.34–1.62 ct | 2,355 stones |
| 7.0 mm | 1.86 ct | 1.53–2.07 ct | 2,365 stones |
| 7.2 mm | 2.00 ct | 1.88–2.29 ct | 150 stones |
| 7.5 mm | 2.07 ct | 1.97–2.53 ct | 3,052 stones |
| 8.0 mm | 2.75 ct | 2.45–3.09 ct | 4,429 stones |
| 9.0 mm | 3.70 ct | 3.06–4.30 ct | 2,583 stones |
| 10.0 mm | 5.07 ct | 4.51–6.07 ct | 1,350 stones |
| 11.0 mm | 7.04 ct | 6.01–8.04 ct | 477 stones |
| 12.0 mm | 8.87 ct | 8.01–10.09 ct | 210 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book where it carries the shape, and are calculated from the trade weight formula where it does not. Covers 2.0 mm to 12.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our cushion (square) buying guide.
Cushion (elongated) diamond size chart
| Length × width | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 × 1.5 mm | 0.025 ct | — | Calculated |
| 2.5 × 1.9 mm | 0.05 ct | — | Calculated |
| 3.0 × 2.3 mm | 0.086 ct | — | Calculated |
| 3.5 × 2.7 mm | 0.14 ct | — | Calculated |
| 4.0 × 3.1 mm | 0.20 ct | — | Calculated |
| 4.5 × 3.4 mm | 0.30 ct | 0.30–0.33 ct | 113 stones |
| 5.0 × 3.9 mm | 0.45 ct | 0.38–0.51 ct | 281 stones |
| 5.3 × 4.1 mm | 0.50 ct | 0.47–0.70 ct | 121 stones |
| 5.5 × 4.2 mm | 0.53 ct | 0.47–0.70 ct | 504 stones |
| 6.0 × 4.6 mm | 0.70 ct | 0.61–0.88 ct | 764 stones |
| 6.5 × 5.1 mm | 1.00 ct | 0.78–1.04 ct | 1,175 stones |
| 7.0 × 5.4 mm | 1.05 ct | 1.00–1.20 ct | 1,610 stones |
| 7.5 × 5.8 mm | 1.50 ct | 1.21–1.57 ct | 884 stones |
| 8.0 × 6.2 mm | 1.70 ct | 1.51–2.04 ct | 1,836 stones |
| 8.5 × 6.5 mm | 2.00 ct | 1.76–2.15 ct | 114 stones |
| 9.0 × 6.9 mm | 2.22 ct | 2.02–2.59 ct | 5,060 stones |
| 10.0 × 7.6 mm | 3.07 ct | 2.64–3.40 ct | 4,287 stones |
| 11.0 × 8.4 mm | 4.07 ct | 3.69–4.94 ct | 1,637 stones |
| 12.0 × 9.0 mm | 5.07 ct | 4.64–6.01 ct | 969 stones |
| 13.0 × 10.0 mm | 7.08 ct | 6.10–8.18 ct | 217 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book where it carries the shape, and are calculated from the trade weight formula where it does not. Covers 2.0 mm to 13.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our cushion (elongated) buying guide.
Emerald diamond size chart
| Length × width | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 × 1.4 mm | 0.03 ct | — | Calculated |
| 2.5 × 1.8 mm | 0.058 ct | — | Calculated |
| 3.0 × 2.3 mm | 0.10 ct | — | Supplier measurement |
| 3.8 × 2.6 mm | 0.17 ct | — | Supplier measurement |
| 4.0 × 3.0 mm | 0.24 ct | — | Supplier measurement |
| 4.5 × 3.2 mm | 0.30 ct | 0.30–0.33 ct | 79 stones |
| 4.7 × 3.4 mm | 0.33 ct | 0.31–0.38 ct | 120 stones |
| 4.9 × 3.5 mm | 0.40 ct | 0.36–0.42 ct | 120 stones |
| 5.0 × 3.6 mm | 0.45 ct | 0.40–0.50 ct | 425 stones |
| 5.3 × 3.8 mm | 0.50 ct | 0.43–0.51 ct | 271 stones |
| 5.5 × 3.9 mm | 0.53 ct | 0.48–0.61 ct | 1,053 stones |
| 6.0 × 4.3 mm | 0.71 ct | 0.66–0.80 ct | 1,490 stones |
| 6.5 × 4.7 mm | 1.00 ct | 0.84–1.03 ct | 3,520 stones |
| 7.0 × 4.9 mm | 1.06 ct | 1.01–1.20 ct | 2,957 stones |
| 7.5 × 5.4 mm | 1.51 ct | 1.33–1.57 ct | 2,846 stones |
| 8.0 × 5.7 mm | 1.70 ct | 1.53–2.05 ct | 4,548 stones |
| 8.4 × 6.0 mm | 2.00 ct | 1.89–2.12 ct | 173 stones |
| 9.0 × 6.4 mm | 2.51 ct | 2.04–2.80 ct | 4,915 stones |
| 9.6 × 6.8 mm | 3.00 ct | 2.89–3.11 ct | 104 stones |
| 10.0 × 6.9 mm | 3.09 ct | 3.01–3.58 ct | 4,897 stones |
| 11.0 × 7.6 mm | 4.10 ct | 4.01–5.04 ct | 2,507 stones |
| 12.0 × 8.3 mm | 5.51 ct | 5.02–6.20 ct | 876 stones |
| 13.0 × 9.1 mm | 7.09 ct | 6.52–8.02 ct | 447 stones |
| 14.0 × 9.8 mm | 9.02 ct | 8.03–10.07 ct | 275 stones |
| 15.0 × 10.4 mm | 10.59 ct | 10.03–12.04 ct | 173 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book where it carries the shape, and are calculated from the trade weight formula where it does not. Covers 2.0 mm to 15.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our emerald buying guide.
Radiant diamond size chart
| Length × width | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 × 1.4 mm | 0.023 ct | — | Calculated |
| 2.5 × 1.8 mm | 0.046 ct | — | Calculated |
| 3.0 × 2.1 mm | 0.079 ct | — | Calculated |
| 3.5 × 2.5 mm | 0.13 ct | — | Calculated |
| 4.0 × 2.8 mm | 0.19 ct | — | Calculated |
| 4.5 × 3.2 mm | 0.27 ct | — | Calculated |
| 4.7 × 3.4 mm | 0.31 ct | 0.30–0.32 ct | 72 stones |
| 5.0 × 3.6 mm | 0.39 ct | 0.35–0.42 ct | 255 stones |
| 5.5 × 4.0 mm | 0.51 ct | 0.45–0.54 ct | 900 stones |
| 6.0 × 4.3 mm | 0.64 ct | 0.54–0.72 ct | 969 stones |
| 6.5 × 4.6 mm | 0.79 ct | 0.71–1.01 ct | 940 stones |
| 7.0 × 5.0 mm | 1.04 ct | 0.97–1.10 ct | 3,346 stones |
| 7.5 × 5.2 mm | 1.19 ct | 1.06–1.51 ct | 1,669 stones |
| 8.0 × 5.8 mm | 1.56 ct | 1.48–1.79 ct | 4,393 stones |
| 8.8 × 6.3 mm | 2.00 ct | 1.92–2.50 ct | 150 stones |
| 9.0 × 6.3 mm | 2.06 ct | 1.92–2.50 ct | 6,191 stones |
| 10.0 × 7.2 mm | 3.07 ct | 2.59–3.16 ct | 6,706 stones |
| 11.0 × 7.9 mm | 4.05 ct | 3.59–4.19 ct | 6,542 stones |
| 12.0 × 8.5 mm | 5.03 ct | 4.66–5.21 ct | 3,666 stones |
| 13.0 × 9.1 mm | 6.10 ct | 5.75–7.26 ct | 509 stones |
| 14.0 × 9.8 mm | 8.03 ct | 7.08–9.53 ct | 226 stones |
| 15.0 × 10.6 mm | 10.06 ct | 9.06–11.07 ct | 197 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book where it carries the shape, and are calculated from the trade weight formula where it does not. Covers 2.0 mm to 15.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our radiant buying guide.
Oval diamond size chart
| Length × width | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 × 1.4 mm | 0.019 ct | — | Calculated |
| 2.5 × 1.8 mm | 0.036 ct | — | Calculated |
| 3.0 × 2.2 mm | 0.063 ct | — | Supplier measurement |
| 3.5 × 2.5 mm | 0.09 ct | — | Supplier measurement |
| 3.6 × 2.7 mm | 0.10 ct | — | Supplier measurement |
| 4.0 × 3.0 mm | 0.15 ct | — | Supplier measurement |
| 4.5 × 3.5 mm | 0.20 ct | — | Supplier measurement |
| 4.8 × 3.3 mm | 0.21 ct | — | Supplier measurement |
| 5.0 × 3.7 mm | 0.30 ct | 0.30–0.31 ct | 115 stones |
| 5.5 × 4.0 mm | 0.34 ct | 0.30–0.40 ct | 680 stones |
| 6.0 × 4.3 mm | 0.46 ct | 0.40–0.51 ct | 890 stones |
| 6.3 × 4.5 mm | 0.50 ct | 0.47–0.53 ct | 486 stones |
| 6.5 × 4.6 mm | 0.54 ct | 0.50–0.61 ct | 1,693 stones |
| 7.0 × 5.0 mm | 0.71 ct | 0.62–1.00 ct | 1,569 stones |
| 7.5 × 5.3 mm | 0.91 ct | 0.77–1.07 ct | 2,855 stones |
| 7.9 × 5.6 mm | 1.00 ct | 0.92–1.20 ct | 948 stones |
| 8.0 × 5.8 mm | 1.06 ct | 1.00–1.12 ct | 17,339 stones |
| 9.0 × 6.5 mm | 1.52 ct | 1.42–1.59 ct | 26,636 stones |
| 9.9 × 7.1 mm | 2.00 ct | 1.86–2.44 ct | 400 stones |
| 10.0 × 7.2 mm | 2.04 ct | 1.81–2.14 ct | 13,801 stones |
| 11.0 × 7.8 mm | 2.59 ct | 2.42–3.07 ct | 8,834 stones |
| 11.4 × 8.1 mm | 3.00 ct | 2.94–4.06 ct | 292 stones |
| 12.0 × 8.4 mm | 3.34 ct | 3.01–4.06 ct | 8,013 stones |
| 13.0 × 9.0 mm | 4.06 ct | 3.92–4.53 ct | 6,093 stones |
| 14.0 × 9.8 mm | 5.10 ct | 5.00–6.09 ct | 1,356 stones |
| 15.0 × 10.4 mm | 6.31 ct | 6.02–7.52 ct | 673 stones |
| 16.0 × 11.3 mm | 8.02 ct | 7.04–9.03 ct | 464 stones |
| 17.0 × 11.9 mm | 9.15 ct | 8.58–10.22 ct | 280 stones |
| 18.0 × 12.5 mm | 10.58 ct | 10.02–11.59 ct | 145 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book where it carries the shape, and are calculated from the trade weight formula where it does not. Covers 2.0 mm to 18.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our oval buying guide.
Pear diamond size chart
| Length × width | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 × 1.3 mm | 0.015 ct | — | Calculated |
| 2.5 × 1.7 mm | 0.03 ct | — | Supplier measurement |
| 3.0 × 2.0 mm | 0.05 ct | — | Supplier measurement |
| 3.5 × 2.2 mm | 0.07 ct | — | Supplier measurement |
| 4.0 × 2.8 mm | 0.12 ct | — | Supplier measurement |
| 4.5 × 3.0 mm | 0.15 ct | — | Supplier measurement |
| 5.0 × 3.0 mm | 0.20 ct | — | Supplier measurement |
| 5.5 × 3.7 mm | 0.30 ct | 0.30–0.31 ct | 258 stones |
| 6.0 × 3.8 mm | 0.32 ct | 0.30–0.40 ct | 995 stones |
| 6.5 × 4.2 mm | 0.43 ct | 0.38–0.50 ct | 1,266 stones |
| 6.9 × 4.4 mm | 0.50 ct | 0.49–0.57 ct | 971 stones |
| 7.0 × 4.5 mm | 0.51 ct | 0.49–0.57 ct | 2,356 stones |
| 7.5 × 4.8 mm | 0.70 ct | 0.57–0.72 ct | 1,821 stones |
| 8.0 × 5.2 mm | 0.90 ct | 0.70–1.05 ct | 3,843 stones |
| 8.6 × 5.5 mm | 1.00 ct | 0.94–1.23 ct | 897 stones |
| 9.0 × 5.7 mm | 1.06 ct | 1.00–1.17 ct | 13,308 stones |
| 9.9 × 6.4 mm | 1.50 ct | 1.46–1.68 ct | 547 stones |
| 10.0 × 6.5 mm | 1.56 ct | 1.46–1.68 ct | 9,936 stones |
| 10.9 × 7.0 mm | 2.00 ct | 1.87–2.20 ct | 294 stones |
| 11.0 × 7.1 mm | 2.06 ct | 1.87–2.20 ct | 8,039 stones |
| 12.0 × 7.7 mm | 2.58 ct | 2.37–3.07 ct | 3,846 stones |
| 13.0 × 8.3 mm | 3.26 ct | 3.00–4.08 ct | 2,311 stones |
| 14.0 × 8.9 mm | 4.08 ct | 3.79–5.06 ct | 2,412 stones |
| 15.0 × 9.6 mm | 5.07 ct | 4.87–5.10 ct | 2,499 stones |
| 16.0 × 10.2 mm | 6.05 ct | 5.48–7.03 ct | 369 stones |
| 17.0 × 10.8 mm | 7.08 ct | 6.91–8.33 ct | 297 stones |
| 18.0 × 11.4 mm | 8.26 ct | 8.02–10.05 ct | 246 stones |
| 19.0 × 12.1 mm | 10.05 ct | 9.14–10.73 ct | 153 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book where it carries the shape, and are calculated from the trade weight formula where it does not. Covers 2.0 mm to 19.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our pear buying guide.
Marquise diamond size chart
| Length × width | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 × 1.0 mm | 0.01 ct | — | Calculated |
| 2.5 × 1.3 mm | 0.02 ct | — | Supplier measurement |
| 3.0 × 1.5 mm | 0.04 ct | — | Supplier measurement |
| 3.5 × 1.9 mm | 0.05 ct | — | Supplier measurement |
| 4.0 × 2.0 mm | 0.06 ct | — | Supplier measurement |
| 4.5 × 2.3 mm | 0.09 ct | — | Supplier measurement |
| 5.0 × 2.8 mm | 0.16 ct | — | Supplier measurement |
| 6.0 × 3.3 mm | 0.29 ct | — | Supplier measurement |
| 6.5 × 3.5 mm | 0.30 ct | 0.30–0.32 ct | 154 stones |
| 7.0 × 3.7 mm | 0.33 ct | 0.30–0.40 ct | 402 stones |
| 7.5 × 3.9 mm | 0.41 ct | 0.37–0.50 ct | 471 stones |
| 7.9 × 4.2 mm | 0.50 ct | 0.47–0.60 ct | 258 stones |
| 8.0 × 4.2 mm | 0.51 ct | 0.47–0.60 ct | 775 stones |
| 9.0 × 4.7 mm | 0.70 ct | 0.61–0.81 ct | 1,019 stones |
| 10.0 × 5.3 mm | 1.04 ct | 0.96–1.09 ct | 3,821 stones |
| 11.0 × 6.0 mm | 1.48 ct | 1.22–1.54 ct | 4,188 stones |
| 11.4 × 6.0 mm | 1.50 ct | 1.43–1.54 ct | 464 stones |
| 12.0 × 6.1 mm | 1.57 ct | 1.50–1.77 ct | 2,991 stones |
| 12.7 × 6.6 mm | 2.00 ct | 1.99–2.60 ct | 93 stones |
| 13.0 × 6.7 mm | 2.09 ct | 2.00–2.54 ct | 1,256 stones |
| 14.0 × 7.2 mm | 2.58 ct | 2.51–3.07 ct | 1,481 stones |
| 15.0 × 7.7 mm | 3.09 ct | 3.01–3.65 ct | 704 stones |
| 16.0 × 8.4 mm | 4.04 ct | 3.90–4.10 ct | 1,346 stones |
| 17.0 × 9.0 mm | 5.01 ct | 4.37–5.09 ct | 155 stones |
| 18.0 × 9.3 mm | 5.53 ct | 5.05–6.13 ct | 83 stones |
| 19.0 × 10.1 mm | 7.01 ct | 6.08–7.09 ct | 87 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book where it carries the shape, and are calculated from the trade weight formula where it does not. Covers 2.0 mm to 19.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our marquise buying guide.
Heart diamond size chart
| Length × width | Carat weight | Typical range | Based on |
|---|---|---|---|
| 2.0 × 2.3 mm | 0.034 ct | — | Calculated |
| 2.5 × 2.8 mm | 0.067 ct | — | Calculated |
| 3.0 × 3.4 mm | 0.12 ct | — | Calculated |
| 3.5 × 3.9 mm | 0.18 ct | — | Calculated |
| 4.0 × 4.5 mm | 0.28 ct | — | Calculated |
| 4.6 × 5.2 mm | 0.42 ct | 0.37–0.50 ct | 63 stones |
| 4.9 × 5.6 mm | 0.51 ct | 0.48–0.56 ct | 166 stones |
| 5.0 × 5.7 mm | 0.55 ct | 0.50–0.68 ct | 595 stones |
| 5.5 × 6.2 mm | 0.72 ct | 0.65–0.92 ct | 1,222 stones |
| 6.0 × 6.9 mm | 1.01 ct | 0.90–1.08 ct | 3,195 stones |
| 6.5 × 7.1 mm | 1.07 ct | 1.01–1.30 ct | 3,238 stones |
| 7.0 × 8.0 mm | 1.52 ct | 1.36–1.70 ct | 2,344 stones |
| 7.5 × 8.3 mm | 1.77 ct | 1.53–2.07 ct | 1,989 stones |
| 7.7 × 8.7 mm | 2.00 ct | 2.01–2.83 ct | 184 stones |
| 8.0 × 9.0 mm | 2.12 ct | 2.01–2.83 ct | 2,266 stones |
| 9.0 × 10.0 mm | 3.04 ct | 2.58–3.62 ct | 2,110 stones |
| 10.0 × 11.1 mm | 4.10 ct | 3.59–5.07 ct | 1,144 stones |
| 11.0 × 12.1 mm | 5.50 ct | 5.01–7.02 ct | 488 stones |
| 12.0 × 13.5 mm | 7.73 ct | 6.23–10.01 ct | 261 stones |
| 13.0 × 14.5 mm | 10.01 ct | 8.05–10.95 ct | 184 stones |
Rows from 0.30 ct up are the median of our own GIA and IGI certified stones, with the sample size shown and the typical range being the middle 80% of that bucket. Smaller sizes come from our diamond supplier's own book where it carries the shape, and are calculated from the trade weight formula where it does not. Covers 2.0 mm to 13.0 mm. Snapshot 2026-08-30.
More on choosing this shape in our heart buying guide.
How to measure a diamond
A loose stone can be weighed, so its carat figure is exact. A set stone cannot, which is why measuring is the only way to estimate the weight of a diamond already in a ring — and why jewellers carry a millimetre gauge.
Measure across the top of the stone, at its widest point, and ignore the setting entirely. For a round, one measurement across the girdle is enough. For any fancy shape take two: the long axis and the short axis, at right angles to each other. Digital calipers are more accurate than a gauge plate, but either will get you within a tenth of a millimetre, which is close enough for the tables above.
One honest caveat about what a measurement can tell you. Two stones with identical face-up measurements can differ in weight by ten per cent or more depending on depth and girdle thickness, which is why the tables publish the range most stones fall in rather than a single figure pretending to be exact. If you need the real weight of a set stone, bring it into the Frankston workshop — our valuation service measures it properly and puts it in writing.
Where these figures come from
Most published size charts copy each other, and the errors travel with them — one widely cited chart lists a 1.00 carat pear as 7.7 × 5.7 mm, a ratio of 1.35, which is its oval row. Ours are built from two first-party sources instead.
From 0.30 ct up, each row is the median of real GIA and IGI certified stones in our own inventory, bucketed by face-up length — 630,306 stones across all shapes, with the sample size shown on every row and the middle 80% of each bucket published as the typical range. Below that weight we do not stock loose stones at all, so quoting our own inventory would be quoting nothing; those rows come from our diamond supplier's own book, which is the trade's working reference for melee. The two agree where they meet: the supplier puts a 4.3 mm round at 0.30–0.34 ct, and our certified stones put 4.3 mm at 0.30 ct.
Four shapes — cushion, radiant, asscher and heart — are not carried in that supply book below our stocked floor. Their smallest rows are calculated with the trade-standard weight formula, with the shape factor calibrated against our own measured stones rather than taken raw, and every one of those rows is labelled “Calculated” so you know which figures are which.
This is a snapshot taken on 2026-08-30, not a live feed. Inventory turns over nightly and a published reference chart should not move under a reader without a human approving the change.
Common questions
How many millimetres is a 1 carat diamond?
A 1 carat round brilliant measures about 6.4 mm across, measured from 7,999 certified stones at exactly that weight. Shape changes the answer more than most people expect: a 1 carat oval is around 7.9 × 5.6 mm and a 1 carat emerald cut around 6.6 × 4.7 mm, because elongated shapes spread their weight across the face-up surface rather than down into the pavilion.Why do two diamonds of the same carat weight measure differently?
Carat is weight, not size. A stone cut deep carries weight in its pavilion, below the setting line where the eye never goes, so it measures smaller face-up than a well-proportioned stone of the same weight. Length-to-width ratio does the same thing across shapes — cut longer, a stone gains length and loses width at identical weight. This is why every figure on this page states the ratio it was measured at, and why the certificate's measurements line matters as much as its carat line.What carat weight is a 2 mm diamond?
A 2 mm round diamond weighs about 0.03 ct — roughly three points. Stones this small are melee, used as accents in a halo, a pavé band or the shoulders of a ring rather than as a centre stone. The sizes and weights for melee come from our diamond supplier's own book, because we do not stock loose stones below 0.30 ct and it would be dishonest to quote our own inventory for a size it does not contain.Does doubling the carat weight double the size?
No, and the gap is wider than it looks. A 1 carat round is about 6.4 mm across and a 2 carat round about 8.1 mm — double the weight for roughly 1.7 mm more diameter. Carat grows in three dimensions while the face-up view only shows two, so the visible difference is always smaller than the weight difference suggests. It is one of the strongest arguments for buying just under a magic weight.How do I measure a diamond that is already set?
Measure across the top of the stone with a millimetre gauge or digital calipers, taking the widest point and, for a fancy shape, the long axis and the short axis separately. Do not measure the setting. A set stone cannot be weighed, so a measurement is the only estimate available — enter it in the converter above and it will return the weight the trade would expect at that size, along with the range most stones of that size actually fall in.Where do these diamond sizes come from?
Backed by industry-direct supplier measurements and 630,306 certified stones. Every figure at 0.30 ct and above is the median of GIA and IGI certified stones in our own inventory, with the sample size published on every row. Below that we use our diamond supplier's own book, which is the trade's working reference for melee. Nothing here is copied from another retailer's chart — several of those disagree with each other and at least one publishes its oval measurements in the pear row.
Keep reading
Size is one of four things worth understanding before you buy. Diamond carat covers what the weight actually costs and why prices jump at the magic weights, diamond cut covers why two stones of the same weight can look completely different, and our shape comparison covers look-per-carat across every shape we sell. For sizing a finger rather than a stone, see our ring size chart and converter.