Standard Gem Sizes Chart

Purpose: Mass produced gem settings come in standard sizes. If a gem won’’t fit in a standard setting, a setting should be custom made. This involves much more labor and therefore expense. Bear this in mind when purchasing a gem, or selecting a cut for a gem. There are circumstances where the value of a stone makes it worth cutting for maximum yield, then later paying for a custom setting. In other circumstances, the cost of a custom setting isn’’t justified by the value of the gemstone.

Sizes: A gem does not need to be the precise size of the setting. A skilled metalsmith can modify a setting to accommodate a wide variety of gem sizes. Any round gem can be put in a standard setting. On other shapes there are a variety of factors to be considered. As a general rule, gems under one carat can be within .1 mm of the setting size. Over one carat, a .2 mm variance can usually be accommodated and sometimes more.

Weights: The weights given are for diamonds cut to ideal proportions. Colored stones are usually cut with greater volume than diamonds, hence they will weigh more than the chart sizes. The density 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 a specific gravity of 3.52,) will weigh 1 carat. A sapphire, (specific gravity 4,) will weigh 1.14 carats. The opal, (specific gravity 2.15) will only weigh .61 carats. There are subtle variations to this list. For example, some list a .25 carat diamond as measuring 4.1 mm. The point is not to take these figures too literally, but to use them as a starting point for estimating weights.


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



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