Millimeters or carats? Choosing a stone size
Carats measure weight. Millimeters measure what you actually see. A setting is made for a diameter, not a weight, so when you buy a loose stone for a ring or pendant, start from millimeters.
The same diameter can weigh quite different amounts. Denser gems such as sapphire weigh more than topaz at the same size, and a deep cut weighs more than a shallow one. That is why our listings give millimeters first.
Round stones: size and approximate weight
Topaz is close to diamond in density, so the figures below hold for both. Treat them as a guide, not a promise: each stone’s actual weight depends on its cut.
| Diameter | Approx. weight | Typical use |
|---|---|---|
| 6 mm | 0.8 ct | Studs, small pendant |
| 7 mm | 1.3 ct | Everyday ring |
| 8 mm | 2 ct | Statement ring, pendant |
| 9 mm | 2.8 ct | Cocktail ring |
| 10 mm | 3.8 ct | Cocktail ring, large pendant |
| 12 mm | 6.5 ct | Centerpiece pendant |
| 14 mm | 10 ct | Collector piece |
A quick way to picture it
Print a ruler or use one at home: 6 mm is about the width of a pencil eraser, 10 mm about the width of a fingernail on a small finger.
If you are matching a setting you already have, measure the inside of the seat, or ask your jeweler for the exact size, and send it to us. We can cut to within 0.1 mm.