Standard Gem Sizes Chart

Will your gem fit in a standard setting? Use this chart of standard gem sizes for popular cuts and also learn how to estimate gem weight based on size.

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Mass-produced jewelry settings come in standard gem sizes. If a gem won''t fit in a standard setting, you should have a setting custom made. However, this involves much more labor and, therefore, expense. When purchasing a gem or selecting a cut design, bear this in mind.
emerald cut tourmaline - standard gem sizes
Although named after the emerald, which often receives this rectangular cut with trimmed corners, the popular emerald cut design can be applied to many gemstones. It has a range of standard gem sizes for mass-produced jewelry settings. Emerald-cut tourmaline, 4.52 cts, slight color shift. © All That Glitters. Used with permission.

Choosing a Standard Setting or a Custom Setting

Under some circumstances, the stone's value makes cutting for maximum yield worthwhile. You can then pay for a custom setting later. However, in other circumstances, the gem's value doesn't justify the cost of a custom setting.

Do Gems Need to Match Standard Settings Precisely?

No, a gem doesn't need to be the precise size of the jewelry setting. A skilled metalsmith can modify a standard setting to accommodate a variety of gem sizes. For example, any round gem can be put in a standard setting. For other shapes, metalsmiths must consider a variety of factors. As a general rule, gems under one carat can fall within 0.1 mm of the setting size. Over one carat, a 0.2 mm variance can usually be accommodated, sometimes more.

Estimating Weights for Gemstones

The carat weights given for standard gem sizes in the following chart apply to diamonds cut to ideal proportions. Typically, gem cutters cut colored gemstones with greater volume than diamonds. Thus, they'll weigh more than the sizes on the chart.

The density or specific gravity (SG) of the material will also affect the weight. For example, a 6.5 mm round diamond, sapphire, and opal, all cut in the same proportions, will all weigh different. The diamond, with an SG of 3.52, will weigh 1 carat. The sapphire, with an SG of 4, will weigh 1.14 carats. The opal, with an SG of 2.15, will only weigh 0.61 carats. (If you know your gemstone density values well, you can estimate the weight of a standard size gem by sight).

There are subtle variations to these values. For example, some charts list a 0.25-carat round diamond as measuring 4.1 mm. Just keep this in mind: don't take these figures too literally. Use this information as a starting point for estimating weights.

Standard Gem Sizes

1.6 mm.02 carat5 mm.75 carat5 x 3 mm.25 carat
2 mm.03 carat6 mm1.3 carat6 x 4 mm.5 carat
2.5 mm.06 carat7 mm2.05 carat7 x 5 mm1.0 carat
3 mm.10 carat8 mm2.9 carat8 x 6 mm1.5 carat
3.5 mm.16 carat9 mm4.4 carat9 x 7 mm2.5 carat
4 mm.25 carat10 mm6.0 carat10 x 8 mm3.0 carat
4.5 mm.33 carat11 mm8.0 carat11 x 9 mm4.0 carat
5 mm.50 carat12 mm10.35 carat12 x 10 mm5.0 carat
5.5 mm.65 carat13 mm13.2 carat14 x 10 mm6.0 carat
6 mm.75 carat14 mm16.5 carat14 x 12 mm8.0 carat
6.5 mm1.0 carat15 mm20.25 carat16 x 12 mm10.5 carat
7 mm1.25 carat16 mm24.6 carat18 x 13 mm14.2 carat
8 mm2.0 carat20 x 15 mm20.3 carat
9 mm2.75 carat22 x 15 mm23.5 carat
10 mm3.5 carat23 x 17 mm32.2 carat
11 mm4.6 carat25 x 18 mm43.0 carat
12 mm6.0 carat27 x 20 mm58.5 carat
13 mm7.75 carat30 x 22 mm79.6 carat
14 mm9.65 carat
15 mm11.85 carat
16 mm14.35 carat
17 mm17.25 carat
18 mm20.5 carat
19 mm24.0 carat
20 mm28.0 carat
21 mm34.8 carat
22 mm41.8 carat
23 mm49.8 carat
24 mm57.9 carat
25 mm68.7 carat
6 x 4 mm.5 carat6 x 5 mm.7 carat4 x 2 mm.10 carat
7 x 5 mm1.0 carat7 x 5 mm.75 carat5 x 2.5 mm.25 carat
8 x 6 mm1.5 carat8 x 5 mm1.0 carat6 x 3 mm.30 carat
9 x 7 mm2.5 carat9 x 6 mm1.5 carat8 x 4 mm.75 carat
10 x 8 mm3.0 carat10 x 7 mm2.0 carat10 x 5 mm1.0 carat
11 x 9 mm4.0 carat11 x 7 mm2.25 carat12 x 6 mm2.0 carat
12 x 10 mm5.0 carat12 x 8 mm3.0 carat14 x 7 mm3.0 carat
14 x 10 mm6.0 carat13 x 9 mm3.5 carat16 x 8 mm4.0 carat
14 x 12 mm8.0 carat15 x 10 mm5.5 carat18 x 9 mm6.0 carat
16 x 12 mm10.5 carat16 x 12 mm8.6 carat20 x 10 mm8.5 carat
18 x 13 mm14.2 carat18 x 13 mm12 carat
20 x 15 mm20.3 carat20 x 15 mm17.3 carat
25 x 18 mm52.2 carat22 x 15 mm18.7 carat
25 x 18 mm30.6 carat
30 x 22 mm54.5 carat

For more information on these gem cuts, consult our guide to fancy gem cuts.

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