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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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
Rounds | Squares | Ovals | |||
Size | Weight | Size | Weight | Size | Weight |
1.6 mm | .02 carat | 5 mm | .75 carat | 5 x 3 mm | .25 carat |
2 mm | .03 carat | 6 mm | 1.3 carat | 6 x 4 mm | .5 carat |
2.5 mm | .06 carat | 7 mm | 2.05 carat | 7 x 5 mm | 1.0 carat |
3 mm | .10 carat | 8 mm | 2.9 carat | 8 x 6 mm | 1.5 carat |
3.5 mm | .16 carat | 9 mm | 4.4 carat | 9 x 7 mm | 2.5 carat |
4 mm | .25 carat | 10 mm | 6.0 carat | 10 x 8 mm | 3.0 carat |
4.5 mm | .33 carat | 11 mm | 8.0 carat | 11 x 9 mm | 4.0 carat |
5 mm | .50 carat | 12 mm | 10.35 carat | 12 x 10 mm | 5.0 carat |
5.5 mm | .65 carat | 13 mm | 13.2 carat | 14 x 10 mm | 6.0 carat |
6 mm | .75 carat | 14 mm | 16.5 carat | 14 x 12 mm | 8.0 carat |
6.5 mm | 1.0 carat | 15 mm | 20.25 carat | 16 x 12 mm | 10.5 carat |
7 mm | 1.25 carat | 16 mm | 24.6 carat | 18 x 13 mm | 14.2 carat |
8 mm | 2.0 carat | 20 x 15 mm | 20.3 carat | ||
9 mm | 2.75 carat | 22 x 15 mm | 23.5 carat | ||
10 mm | 3.5 carat | 23 x 17 mm | 32.2 carat | ||
11 mm | 4.6 carat | 25 x 18 mm | 43.0 carat | ||
12 mm | 6.0 carat | 27 x 20 mm | 58.5 carat | ||
13 mm | 7.75 carat | 30 x 22 mm | 79.6 carat | ||
14 mm | 9.65 carat | ||||
15 mm | 11.85 carat | ||||
16 mm | 14.35 carat | ||||
17 mm | 17.25 carat | ||||
18 mm | 20.5 carat | ||||
19 mm | 24.0 carat | ||||
20 mm | 28.0 carat | ||||
21 mm | 34.8 carat | ||||
22 mm | 41.8 carat | ||||
23 mm | 49.8 carat | ||||
24 mm | 57.9 carat | ||||
25 mm | 68.7 carat |
Emerald | Pear | Marquis | |||
6 x 4 mm | .5 carat | 6 x 5 mm | .7 carat | 4 x 2 mm | .10 carat |
7 x 5 mm | 1.0 carat | 7 x 5 mm | .75 carat | 5 x 2.5 mm | .25 carat |
8 x 6 mm | 1.5 carat | 8 x 5 mm | 1.0 carat | 6 x 3 mm | .30 carat |
9 x 7 mm | 2.5 carat | 9 x 6 mm | 1.5 carat | 8 x 4 mm | .75 carat |
10 x 8 mm | 3.0 carat | 10 x 7 mm | 2.0 carat | 10 x 5 mm | 1.0 carat |
11 x 9 mm | 4.0 carat | 11 x 7 mm | 2.25 carat | 12 x 6 mm | 2.0 carat |
12 x 10 mm | 5.0 carat | 12 x 8 mm | 3.0 carat | 14 x 7 mm | 3.0 carat |
14 x 10 mm | 6.0 carat | 13 x 9 mm | 3.5 carat | 16 x 8 mm | 4.0 carat |
14 x 12 mm | 8.0 carat | 15 x 10 mm | 5.5 carat | 18 x 9 mm | 6.0 carat |
16 x 12 mm | 10.5 carat | 16 x 12 mm | 8.6 carat | 20 x 10 mm | 8.5 carat |
18 x 13 mm | 14.2 carat | 18 x 13 mm | 12 carat | ||
20 x 15 mm | 20.3 carat | 20 x 15 mm | 17.3 carat | ||
25 x 18 mm | 52.2 carat | 22 x 15 mm | 18.7 carat | ||
25 x 18 mm | 30.6 carat | ||||
30 x 22 mm | 54.5 carat |
For more information on these gem cuts, consult our guide to fancy gem cuts.
International Gem Society
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