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: Calibrated Gems: Size to Weight Chart

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

Oval GemstonesOval 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 GemstonesRound 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 GemstonesPear 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 GemstonesOctagon / 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 GemstonesMarquise 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: July-07-2017
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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

Size Comparison Chart