Free tool
Diamond size on your hand
6.50 mmacross, face up
39%of finger width
On a photo of your hand
Add a photo of your hand, then drag the two dots to the edges of your ring finger where a ring sits. The stone appears to scale between them. Drag it to move both.
Your photo stays on this device. Nothing is uploaded.
How big each carat looks
Carat is a weight, not a size: one carat is 200 milligrams. What you see on the hand is the stone's outline from above, so the simulator draws each stone at its face-up size in millimeters, and the finger at the inside diameter of the ring size you pick.
The stone sizes come from DiamDB's charts for typical well cut round, oval, emerald, pear, cushion, radiant, princess and marquise diamonds. Those charts use a length to width ratio of 1.5 for ovals, 1.35 for emeralds, 1.66 for pears and 2 for marquises, and they show cushions and radiants as squares. An elongated cushion or radiant of the same weight is longer and narrower than drawn here.
| Shape | 0.5 ct | 1 ct | 1.5 ct | 2 ct | 3 ct |
|---|---|---|---|---|---|
| Round | 5.16 | 6.5 | 7.44 | 8.19 | 9.37 |
| Oval | 6.44 × 4.29 | 8.12 × 5.41 | 9.29 × 6.19 | 10.23 × 6.82 | 11.7 × 7.8 |
| Emerald | 5.31 × 3.93 | 6.68 × 4.95 | 7.65 × 5.67 | 8.42 × 6.24 | 9.64 × 7.14 |
| Pear | 7.19 × 4.33 | 9.05 × 5.45 | 10.36 × 6.24 | 11.4 × 6.87 | 13.05 × 7.86 |
| Cushion | 4.62 | 5.83 | 6.67 | 7.34 | 8.4 |
| Radiant | 4.59 | 5.78 | 6.61 | 7.28 | 8.33 |
| Princess | 4.37 | 5.51 | 6.31 | 6.94 | 7.95 |
| Marquise | 8.24 × 4.12 | 10.38 × 5.19 | 11.9 × 5.95 | 13.08 × 6.54 | 14.98 × 7.49 |
Face-up size in millimeters, length by width. Square shapes list one side. Source: DiamDB.
Reading the numbers
Finger width here is the ring's inside diameter. US sizes add 0.032 inches (0.81 mm) of diameter per whole size, so a size 6 is 16.5 mm across, the same figure GIA's ring size chart gives. On that finger a 1 carat round covers about 39% of the width, a 1 carat oval about 33% and a 2 carat round about half.
Weight grows faster than size. A 2 carat round weighs twice as much as a 1 carat but is only 26% wider, 8.19 mm against 6.5 mm. Long shapes put their size into length: a 1 carat marquise runs 10.38 mm down the finger. GIA notes that long shapes set north to south can make a finger look longer.
Real stones differ from any chart. A deep cut hides weight below the top, and outlines vary: two GIA graded 1.00 carat ovals in our oval vs round comparison differ by more than 0.4 mm in length, and our carat size chart sets these model sizes next to real graded stones. Compare the millimeters on a stone's grading report, not only its carats.
About the photo option
The photo opens in your browser and stays on your device. There is no upload. The two dots tell the page how many pixels make a millimeter on your photo: it treats the space between them as the inside diameter of the ring size you picked, so set your size first. Fingers are not perfect circles, so read the result as a close guide and confirm your size with a jeweler.