Diamond Carat Size Chart on Hand: 1ct to 3ct by Ring Size
By Jared James · Last updated 28 July 2026
Quick answer
A well-cut round diamond covers about 34 to 43 per cent of the ring's inside diameter at 1 carat and 49 to 62 per cent at 3 carats across US ring sizes 4 to 9. The tables below compare that on-hand scale with face-up measurements for nine shapes. Finger shape, setting and band width still change how large a stone looks.
Carat size chart in mm
Face-up measurements for well-cut stones. Symmetric shapes show one number (length equals width); elongated shapes show length by width at the assumed ratio in brackets. A stone cut deep for weight retention will face up smaller than this table.
| Shape | 1ct | 1.5ct | 2ct | 2.5ct | 3ct |
|---|---|---|---|---|---|
| Round brilliant | 6.4mm | 7.4mm | 8.1mm | 8.7mm | 9.3mm |
| Oval (1.40) | 8.3 x 5.6mm | 9.5 x 6.4mm | 10.5 x 7.0mm | 11.3 x 7.5mm | 12.0 x 8.0mm |
| Cushion (1.00) | 6.0mm | 6.8mm | 7.5mm | 8.1mm | 8.6mm |
| Princess (1.00) | 5.6mm | 6.4mm | 7.0mm | 7.5mm | 8.0mm |
| Emerald cut (1.40) | 7.1 x 5.2mm | 8.2 x 5.9mm | 9.0 x 6.5mm | 9.7 x 7.0mm | 10.3 x 7.4mm |
| Asscher (1.00) | 5.6mm | 6.4mm | 7.0mm | 7.5mm | 8.0mm |
| Pear (1.50) | 8.7 x 5.6mm | 10.0 x 6.4mm | 11.0 x 7.0mm | 11.8 x 7.5mm | 12.6 x 8.0mm |
| Marquise (2.00) | 10.3 x 5.2mm | 11.8 x 5.9mm | 13.0 x 6.5mm | 14.0 x 7.0mm | 14.9 x 7.4mm |
| Radiant (1.10) | 6.3 x 5.2mm | 7.3 x 5.9mm | 8.0 x 6.5mm | 8.6 x 7.0mm | 9.2 x 7.4mm |
All values are approximate. The measurements line on an individual grading report is the final word for any specific stone.
Diamond Carat Size on Hand by Ring Size
This table uses the diameter of a typical round brilliant at each weight and divides it by the standard inside diameter for US ring sizes 4 to 9. It gives one repeatable way to compare finger coverage. It is not a promise about appearance, because the outside width of a finger, knuckle shape, setting height and band width all change the result.
| US ring size | Inside diameter | 1ct round | 1.5ct round | 2ct round | 2.5ct round | 3ct round |
|---|---|---|---|---|---|---|
| 4 | 14.9mm | 43% | 50% | 54% | 58% | 62% |
| 5 | 15.7mm | 41% | 47% | 52% | 55% | 59% |
| 6 | 16.5mm | 39% | 45% | 49% | 53% | 56% |
| 7 | 17.3mm | 37% | 43% | 47% | 50% | 54% |
| 8 | 18.1mm | 35% | 41% | 45% | 48% | 51% |
| 9 | 18.9mm | 34% | 39% | 43% | 46% | 49% |
Percentages show the round diamond's width against the ring's inside diameter. Elongated shapes cover more length along the finger and may look larger even when their width is similar.
Is 2 or 3 Carats Too Big for My Finger?
Two carats is not automatically too big for a size 4 finger. A round 2ct stone is about 8.1mm wide, roughly 54 per cent of that ring's inside diameter, so it will look prominent. On a size 9 finger the same stone is about 43 per cent of the inside diameter and reads less dominant.
Three carats covers about 62 per cent of a size 4 ring's inside diameter and 49 per cent of a size 9. Setting height, shape and lifestyle decide whether that feels wearable. Draw the measurements on paper, try the outline against the hand and check how a similarly sized setting behaves when making a fist or putting a hand in a pocket.
Round sizes at one scale
Check the size on paper
The most reliable way to preview a carat size is to draw it. Take a ruler with mm markings, draw a circle or rectangle at the measurements from the chart, cut it out and hold it against your finger. Paper does not lie the way screens do.
If you prefer to print, our ring size chart page includes a printable sizer PDF with a built-in check ruler; print at 100% scale, confirm the check ruler measures true, and anything else you print at the same setting will be true to size as well.
Why carat is not a size
Carat measures weight: one carat is 200 milligrams. The size you see on the hand is the face-up area, and the two are related but not interchangeable. Weight grows with volume, so doubling the carat adds roughly 26% to each dimension rather than doubling the width, and part of every extra carat disappears into the depth of the stone where you cannot see it.
Shape moves the equation more than most buyers expect. At every weight in the chart, the marquise is the longest stone and the princess and Asscher are the most compact, because elongated shapes spread their weight thin and square shapes stack it deep. Cut quality matters too: two stones with identical weight and ratio can differ by a few tenths of a millimetre face up depending on how well they are cut.
Size guides by weight
- #01
How big is a 1 carat diamond?
The 1ct size in mm for every shape, on the hand and next to 2 carats at one scale.
- #02
How big is a 2 carat diamond?
The 2ct size table with on-hand photos and AUD price bands.
- #03
Is a 3 carat diamond big?
The 3ct size in mm for every shape and how a stone that size wears day to day.
- #04
What diamond carat weight really means
Why carat is weight rather than size, and how cut changes what you see.
What each weight costs
See them in a setting
Compare carat sizes in real rings
Browse lab-grown diamond engagement rings across every shape and carat weight, made to order in Melbourne.
View lab-grown ringsFrequently asked questions
- Is carat a size or a weight?
- A weight. One carat is 200 milligrams. Two diamonds of the same carat weight can face up at different sizes depending on their shape, their length-to-width ratio and how deep they were cut, which is why the mm measurements on a grading report matter more than the carat number alone.
- How many mm is a 1 carat diamond?
- A well-cut 1 carat round brilliant measures about 6.4mm across. The same weight in an oval is about 8.3mm long, and a 1 carat marquise stretches to about 10.3mm.
- How many mm is a 2 carat diamond?
- A well-cut 2 carat round brilliant measures about 8.1mm across. A 2 carat oval is about 10.5mm by 7.0mm, and a 2 carat emerald cut about 9.0mm by 6.5mm.
- How many mm is a 3 carat diamond?
- A well-cut 3 carat round brilliant measures about 9.3mm across. A 3 carat oval is about 12.0mm by 8.0mm, and a 3 carat pear about 12.6mm long.
- Why does doubling the carat not double the size?
- Because weight grows with volume while the size you see is an area. Doubling the weight from 1 to 2 carats makes a round diamond about 27% wider and gives it about 60% more face-up area, not twice as much. The extra weight also sits partly in the depth of the stone.
- Are the sizes in this chart exact?
- No, they are typical measurements for well-cut stones at the listed length-to-width ratio. A deep-cut diamond hides weight underneath and faces up smaller, and a different ratio moves both numbers. Always check the measurements line on the individual grading report.
Want to compare stones
Not sure which carat weight suits the hand?
Send us a note with the finger size and the shapes you like, and we will show you real stones at each weight.
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