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Calibrated Size Charts for Gemstones to be set in Standard Jewelry Mountings

The weights given are for diamonds cut to ideal proportions. Colored stones are usually cut with greater volume than diamonds; therefore, 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 have different weights. 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.

Oval Gemstones

Oval Cut

Calibrated Size Chart for Standard Jewelry Mountings (approximate weights)

Size in mm Weight in carat

5x3 6x4 7x5 8x6 9x7 10x8 11x9 12x10 14x12
Alexandrite .30 .51 .80 1.45 2.00 3.60 4.25 6.00 8.90
Amethyst .23 .45 .85 1.25 1.75 2.40 3.20 4.50 6.50
Aquamarine .20 .40 .75 1.10 1.75 2.25 3.00 4.50 6.75
Citrine .23 .45 .85 1.25 1.75 2.40 3.25 4.20 5.20
Diamond .25 .50 .75 1.40 2.00 3.00 4.00 5.00 8.00
Emerald .25 .52 .85 1.26 1.90 2.60 3.75 5.00 7.50
Pyrope Garnet .25 .55 1.00 1.40 2.10 2.80 3.75 5.00 7.00
Iolite .21 .40 .63 1.02 - - - - -
Opal .16 .28 .47 .78 1.10 1.65 2.15 3.00 4.00
Peridot .28 .50 .95 1.35 2.00 2.50 3.50 4.00 6.00
Ruby .35 .60 1.06 1.55 2.20 3.15 3.80 6.00 7.25
Sapphire .35 .60 1.00 1.55 2.20 3.15 3.80 6.00 7.25
Tanzanite .20 .48 .89 1.35 - - - - -
Topaz .28 .57 1.10 1.60 2.50 3.50 4.50 6.00 8.80
Tourmaline .25 .50 .90 1.18 2.30 2.90 3.50 5.25 6.80
Tsavorite .28 .52 .75 - - - - - -
Zircon .40 .75 1.45 2.00 2.85 4.00 5.60 7.50 8.20
Round Gemstones

Round Cut

Calibrated Size Chart for Standard Jewelry Mountings (approximate weights)

Size in mm Weight in carat

2 3 4 5 6 6.5 7 8 10
Alexandrite .04 .12 .35 .63 1.30 1.86 2.15 2.90 5.20
Amethyst .04 .10 .20 .40 .70 1.10 1.30 1.80 3.30
Aquamarine .04 .10 .25 .45 .75 1.31 1.60 2.40 3.50
Citrine .04 .10 .20 .40 .70 1.10 1.30 1.80 3.30
Diamond .03 .10 .23 .47 .80 1.00 1.25 1.90 3.50
Emerald .04 .12 .27 .48 .80 1.26 1.70 2.50 6.10
Pyrope Garnet .05 .13 .30 .60 1.00 1.40 1.60 2.50 5.75
Opal .02 .09 .16 .34 .57 .75 .83 1.30 2.00
Peridot .05 .12 .26 .50 .85 1.11 1.25 2.00 5.25
Ruby .05 .15 .34 .65 1.05 1.41 1.60 2.25 4.50
Sapphire .05 .15 .34 .65 1.05 1.41 1.60 2.25 4.50
Topaz .04 .11 .30 .56 1.00 1.36 1.55 2.50 5.75
Tourmaline .04 .12 .24 .45 .75 1.28 1.55 2.00 3.00
Zircon .06 .17 .36 .69 1.25 1.58 1.75 2.60 5.00
Pear Gemstones

Pear Cut

Calibrated Size Chart for Standard Jewelry Mountings (approximate weights)

Size in mm Weight in carat

5x3 6x4 7x5 8x6 9x6 10x7 12x8 14x9  
Alexandrite .30 .50 .85 1.10 2.10 3.60 6.60 8.80  
Amethyst .20 .35 .65 .85 1.25 1.70 4.00 5.00  
Aquamarine .20 .35 .65 .90 1.30 1.85 4.20 5.60  
Citrine .20 .35 .65 .85 1.30 1.70 4.00 5.00  
Diamond .25 .50 .75 1.00 1.50 2.00 3.50 5.00  
Emerald .25 .45 .70 1.05 1.70 2.60 4.15 6.10  
Pyrope Garnet .25 .40 1.00 1.15 1.30 1.80 3.50 5.80  
Opal .13 .22 .35 .50 .70 1.03 1.40 2.45  
Peridot .25 .45 .70 .80 1.10 1.40 3.40 4.75  
Ruby .30 .50 .75 1.00 1.85 2.50 4.75 7.90  
Sapphire .30 .50 .75 1.00 1.85 2.50 4.75 7.90  
Topaz .25 .50 1.00 1.10 2.00 3.50 6.50 8.50  
Tourmaline .35 .45 .60 .90 1.10 1.40 2.80 6.75  
Zircon .30 .70 1.00 1.30 2.60 4.00 5.25 7.50  
Octagon Gemstones

Octagon / Emerald Cut

Calibrated Size Chart for Standard Jewelry Mountings (approximate weights)

Size in mm Weight in carat

5x3 6x4 7x5 8x6 9x7 10x8 11x9 12x10 14x12
Alexandrite .40 .70 1.30 2.60 3.60 4.20 6.00 8.50 9.90
Amethyst .35 .55 1.10 1.60 2.25 2.90 4.20 5.60 7.25
Aquamarine .25 .50 .80 1.40 2.00 3.00 4.30 4.75 7.75
Citrine .35 .55 1.00 1.60 2.25 2.90 4.20 5.60 7.25
Diamond .25 .50 1.00 1.50 3.00 4.00 5.00 7.80 8.80
Emerald .30 .60 .90 1.80 2.31 3.15 4.50 5.25 5.80
Pyrope Garnet .40 .80 1.20 1.70 2.50 3.50 4.30 6.35 9.00
Peridot .35 .60 1.00 1.70 2.25 3.80 5.25 6.25 8.80
Ruby .55 .75 1.15 1.60 2.30 2.75 4.00 6.25 9.00
Sapphire .55 .75 1.15 1.75 2.30 2.75 4.00 6.25 9.00
Topaz .40 .65 1.25 2.40 3.40 4.00 5.75 8.00 9.50
Tourmaline .30 .60 1.60 2.15 2.80 3.60 4.30 5.20 8.50
Zircon .60 .85 1.70 2.35 3.90 450 6.20 7.01 8.95
Marquise Gemstones

Marquise Cut

Calibrated Size Chart for Standard Jewelry Mountings (approximate weights)

Size in mm Weight in carat

4x2 5x3 6x3 7x3.5 8x4 10x5 12x6 14x7  
Alexandrite .07 .20 .30 .50 .70 1.25 2.10 3.50  
Amethyst .10 .15 .20 .34 .48 .90 1.59 2.45  
Aquamarine .08 .14 .20 .25 .50 .80 1.50 2.75  
Citrine .10 .15 .20 .35 .50 .90 1.59 2.45  
Diamond .12 .18 .25 .37 .50 1.00 2.00 3.00  
Emerald .09 .19 .30 .45 .60 1.40 1.80 2.80  
Pyrope Garnet .09 .16 .25 .42 .60 1.20 2.00 2.85  
Opal .09 .13 .17 .27 .37 .59 1.00 1.25  
Peridot .10 .17 .25 .37 .50 1.00 2.00 2.55  
Ruby .13 .24 .35 .55 .75 1.15 2.20 3.00  
Sapphire .13 .24 .35 .55 .75 1.15 2.20 3.00  
Topaz .07 .17 .30 .50 .70 1.20 2.00 3.40  
Tourmaline .10 .20 .30 .45 .60 .85 1.55 2.20  
Zircon .13 .23 .33 .55 .75 1.25 1.95 3.00  
  • First Published: February-20-2006
  • Last Updated: May-31-2022
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Size and Weight

Gems are always measured in Millimeter (mm)

Dimensions are given as;
length x width x depth,
except for round stones which are;
diameter x depth

Select gems by size, not by weight!
Gem varieties vary in density, so carat weight is not a good indication of size

Note: 1ct = 0.2g

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