Standard Gem Sizes Chart: Guide to Gemstone Dimensions

In this article, you will learn:

• How to determine whether to choose a standard or a custom made  setting for your gemstone.
• The flexibility of standard settings and how much size variance they can accommodate.
• Methods for estimating gemstone weights based on dimensions and material properties.
• Standard gemstone sizes for various cut designs.

Choosing Between Standard vs Custom Gemstone Settings

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 Standard Jewelry Settings Require Exact Gem Sizes?

No, your gemstone doesn't need to precisely match the jewelry setting size. A skilled metalsmith can modify standard settings to accommodate various gem sizes. When considering setting options:

• Any round gemstone can typically be placed in a standard setting regardless of exact dimensions.
• For other gemstone shapes, metalsmiths must evaluate multiple factors before modification.
• Gems under one carat can generally fall within 0.1 mm of the setting size.
• Gemstones over one carat usually accommodate a 0.2 mm variance, sometimes more.

How to Estimate Gemstone Weights Based on Size

The carat weights provided in standard gem sizes charts apply to diamonds cut to ideal proportions. Typically, gem cutters shape colored gemstones with greater volume than diamonds, resulting in heavier weights than standard chart measurements.

The density or specific gravity of the material significantly affects the weight. For example:

• A 6.5 mm round diamond with an SG of 3.52 will weigh 1 carat.
• A 6.5 mm round sapphire with an SG of 4 will weigh 1.14 carats.
• A 6.5 mm round opal with an SG of 2.15 will only weigh 0.61 carats.

If you're familiar with gemstone density values, you can estimate the weight of a standard size gem by sight. Remember that subtle variations exist in these measurements. Some charts might list a 0.25-carat round diamond as 4.1 mm. Use this information as a starting point rather than absolute values.

Standard Gem Sizes Chart for Popular Cuts

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 detailed information on various gemstone cuts, consult our guide to fancy gem cuts. Standard gem sizes charts help jewelers and customers understand the typical dimensions for different gemstone weights and cuts.