MM to Carat Weight Conversion Charts

CONVERSION CHARTS

Use these charts to look up the approximate carat weight
of your favorite gemstone by measuring the MM size

Round Gemstones

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

Marquise Faceted Gemstone Weight Chart (Weights are approximate)
	4x2mm	5x3mm	6x3mm	7x3.5mm	8x4mm	10x5mm	12x6mm	14x7mm
Alexandrite	.07 ct	.20 ct	.30 ct	.50 ct	.70 ct	1.25 ct	2.10 ct	3.50 ct
Amethyst	.10 ct	.15 ct	.20 ct	.34 ct	.48 ct	.90 ct	1.59 ct	2.45 ct
Aquamarine	.08 ct	.14 ct	.20 ct	.25 ct	.50 ct	.80 ct	1.50 ct	2.75 ct
Citrine	.10 ct	.15 ct	.20 ct	.35 ct	.50 ct	.90 ct	1.59 ct	2.45 ct
Diamond	.12 ct	.18 ct	.25 ct	.37 ct	.50 ct	1.00 ct	2.00 ct	3.00 ct
Emerald	.09 ct	.19 ct	.30 ct	.45 ct	.60 ct	1.40 ct	1.80 ct	2.80 ct
Garnet	.09 ct	.16 ct	.25 ct	.42 ct	.60 ct	1.20 ct	2.00 ct	2.85 ct
Opal	.09 ct	.13 ct	.17 ct	.27 ct	.37 ct	.59 ct	1.00 ct	1.25 ct
Peridot	.10 ct	.17 ct	.25 ct	.37 ct	.50 ct	1.00 ct	2.00 ct	2.55 ct
Ruby	.13 ct	.24 ct	.35 ct	.55 ct	.75 ct	1.15 ct	2.20 ct	3.00 ct
Sapphire	.13 ct	.24 ct	.35 ct	.55 ct	.75 ct	1.15 ct	2.20 ct	3.00 ct
Topaz	.07 ct	.17 ct	.30 ct	.50 ct	.70 ct	1.20 ct	2.00 ct	3.40 ct
Tourmaline	.10 ct	.20 ct	.30 ct	.45 ct	.60 ct	.85 ct	1.55 ct	2.20 ct
Zircon	.13 ct	.23 ct	.33 ct	.55 ct	.75 ct	1.25 ct	1.95 ct	3.00 ct

Octagon Cut

Octagon Faceted Gemstone Weight Chart (approximate weights)
	5x3mm	6x4mm	7x5mm	8x6mm	9x7mm	10x8mm	11x9mm	12x10mm	14x10mm
Alexandrite	.40 ct	.70 ct	1.30 ct	2.60 ct	3.60 ct	4.20 ct	6.00 ct	8.50 ct	9.90 ct
Amethyst	.35 ct	.55 ct	1.00 ct	1.60 ct	2.25 ct	2.90 ct	4.20 ct	5.60 ct	7.25 ct
Aquamarine	.25 ct	.50 ct	.80 ct	1.40 ct	2.00 ct	3.00 ct	4.30 ct	4.75 ct	7.75 ct
Citrine	.35 ct	.55 ct	1.00 ct	1.60 ct	2.25 ct	2.90 ct	4.20 ct	5.60 ct	7.25 ct
Diamond	.25 ct	.50 ct	1.00 ct	1.50 ct	3.00 ct	4.00 ct	5.00 ct	7.80 ct	8.80 ct
Emerald	.30 ct	.60 ct	.90 ct	1.80 ct	2.31 ct	3.15 ct	4.50 ct	5.25 ct	5.80 ct
Garnet	.40 ct	.80 ct	1.20 ct	1.70 ct	2.50 ct	3.50 ct	4.30 ct	6.35 ct	9.00 ct
Peridot	.35 ct	.60 ct	1.00 ct	1.70 ct	2.25 ct	3.80 ct	5.25 ct	6.25 ct	8.80 ct
Ruby	.55 ct	.75 ct	1.15 ct	1.60 ct	2.30 ct	2.75 ct	4.00 ct	6.25 ct	9.00 ct
Sapphire	.55 ct	.75 ct	1.15 ct	1.75 ct	2.30 ct	2.75 ct	4.00 ct	6.25 ct	9.00 ct
Topaz	.40 ct	.65 ct	1.25 ct	2.40 ct	3.40 ct	4.00 ct	5.75 ct	8.00 ct	9.50 ct
Tourmaline	.30 ct	.60 ct	1.60 ct	2.15 ct	2.80 ct	3.60 ct	4.30 ct	5.20 ct	8.50 ct
Zircon	.60 ct	.85 ct	1.70 ct	2.35 ct	3.90 ct	4.50 ct	6.20 ct	7.01 ct	8.95 ct

Oval Cut

Oval Faceted Gemstone Weight Chart (approximate weights)
	5x3mm	6x4mm	7x5mm	8x6mm	9x7mm	10x8mm	11x9mm	12x10mm	14x10mm
Alexandrite	.30 ct	.51 ct	.80 ct	1.45 ct	2.00 ct	3.60 ct	4.25 ct	6.00 ct	8.90 ct
Amethyst	.23 ct	.45 ct	.85 ct	1.25 ct	1.75 ct	2.40 ct	3.20 ct	4.50 ct	6.50 ct
Aquamarine	.20 ct	.40 ct	.75 ct	1.10 ct	1.75 ct	2.25 ct	3.00 ct	4.50 ct	6.75 ct
Citrine	.23 ct	.45 ct	.85 ct	1.25 ct	1.75 ct	2.40 ct	3.25 ct	4.20 ct	5.20 ct
Diamond	.25 ct	.50 ct	.75 ct	1.40 ct	2.00 ct	3.00 ct	4.00 ct	5.00 ct	8.00 ct
Emerald	.25 ct	.52 ct	.85 ct	1.26 ct	1.90 ct	2.60 ct	3.75 ct	5.00 ct	7.50 ct
Garnet, Mozambique	.25 ct	.55 ct	1.00 ct	1.40 ct	2.10 ct	2.80 ct	3.75 ct	5.00 ct	7.00 ct
Garnet, Rhodolite	.25 ct	.55 ct	1.00 ct	1.40 ct	2.10 ct	2.80 ct	-	-	-
Iolite	.21 ct	.40 ct	.63 ct	1.02 ct	-	-	-	-	-
Opal	.16 ct	.28 ct	.47 ct	.78 ct	1.10 ct	1.65 ct	2.15 ct	3.00 ct	4.00 ct
Peridot	.28 ct	.50 ct	.95 ct	1.35 ct	2.00 ct	2.50 ct	3.50 ct	4.00 ct	6.00 ct
Ruby	.35 ct	.60 ct	1.06 ct	1.55 ct	2.20 ct	3.15 ct	3.80 ct	6.00 ct	7.25 ct
Sapphire	.35 ct	.60 ct	1.00 ct	1.55 ct	2.20 ct	3.15 ct	3.80 ct	6.00 ct	7.25 ct
Tanzanite	.20 ct	.48 ct	.89 ct	1.35 ct	-	-	-	-	-
Topaz	.28 ct	.57 ct	1.10 ct	1.60 ct	2.50 ct	3.50 ct	4.50 ct	6.00 ct	8.80 ct
Tourmaline	.25 ct	.50 ct	.90 ct	1.18 ct	2.30 ct	2.90 ct	3.50 ct	5.25 ct	6.80 ct
Tsavorite	.28 ct	.52 ct	.75 ct	-	-	-	-	-	-
Zircon	.40 ct	.75 ct	1.45 ct	2.00 ct	2.85 ct	4.00 ct	5.60 ct	7.50 ct	8.20 ct

Pear Faceted Gemstone Weight Chart (approximate weights)
	5x3mm	6x4mm	7x5mm	8x6mm	9x6mm	10x7mm	12x8mm	14x9mm
Alexandrite	.30 ct	.50 ct	.85 ct	1.10 ct	2.10 ct	3.60 ct	6.60 ct	8.80 ct
Amethyst	.20 ct	.35 ct	.65 ct	.85 ct	1.25 ct	1.70 ct	4.00 ct	5.00 ct
Aquamarine	.20 ct	.35 ct	.65 ct	.90 ct	1.30 ct	1.85 ct	4.20 ct	5.60 ct
Citrine	.20 ct	.35 ct	.65 ct	.85 ct	1.30 ct	1.70 ct	4.00 ct	5.00 ct
Diamond	.25 ct	.50 ct	.75 ct	1.00 ct	1.50 ct	2.00 ct	3.50 ct	5.00 ct
Emerald	.25 ct	.45 ct	.70 ct	1.05 ct	1.70 ct	2.60 ct	4.15 ct	6.10 ct
Garnet	.25 ct	.40 ct	1.00 ct	1.15 ct	1.30 ct	1.80 ct	3.50 ct	5.80 ct
Opal	.13 ct	.22 ct	.35 ct	.50 ct	.70 ct	1.03 ct	1.40 ct	2.45 ct
Peridot	.25 ct	.45 ct	.70 ct	.80 ct	1.10 ct	1.40 ct	3.40 ct	4.75 ct
Ruby	.30 ct	.50 ct	.75 ct	1.00 ct	1.85 ct	2.50 ct	4.75 ct	7.90 ct
Sapphire	.30 ct	.50 ct	.75 ct	1.00 ct	1.85 ct	2.50 ct	4.75 ct	7.90 ct
Topaz	.25 ct	.50 ct	1.00 ct	1.10 ct	2.00 ct	3.50 ct	6.50 ct	8.50 ct
Tourmaline	.35 ct	.45 ct	.60 ct	.90 ct	1.10 ct	1.40 ct	2.80 ct	6.75 ct
Zircon	.30 ct	.70 ct	1.00 ct	1.30 ct	2.60 ct	4.00 ct	5.25 ct	7.50 ct

Diamond Conversion Charts

Diamonds			Diamonds
Round Cut	Decimal Inch		Round Cut	Decimal Inch
mm width	decimal width	Weight	mm width	decimal width	Weight
1.0 mm	.039 inch	.005 carat	4.8 mm		.40 carat
1.2 mm		.008 carat	4.9 mm		.43 carat
1.3 mm		.01 carat	5.0 mm	.197 inch	.47 carat
1.5 mm		.015 carat	5.2 mm	.205 inch	1/2 carat
1.7 mm		.02 carat	5.4 mm		.60 carat
1.8 mm		.025 carat	5.5 mm		.63 carat
2.0 mm	.079 inch	.03 carat	5.6 mm		.65 carat
2.1 mm		.035 carat	5.8 mm	.228 inch	3/4 carat
2.2 mm		.04 carat	6.0 mm	.236 inch	.80 carat
2.4 mm		.05 carat	6.2 mm		.85 carat
2.5 mm		.06 carat	6.4 mm		.95 carat
2.7 mm		.07 carat	6.5 mm	.255 inch or 1/4 inch	1.00 carat
2.8 mm		.08 carat	6.6 mm		1.10 carat
2.9 mm		.09 carat	6.8 mm		1.17 carat
3.0 mm	.118 inch	1/10 carat	7.0 mm	.276 inch	1-1/4 carat
3.1 mm		.11 carat	7.2 mm		1.33 carat
3.2 mm	.125 inch or 1/8 inch	.12 carat	7.4 mm	.291 inch	1-1/2 carat
3.3 mm		.14 carat	7.6 mm		1.60 carat
3.4 mm		.15 carat	7.8 mm	.307 inch	1.75 carat
3.5 mm		.16 carat	8.0 mm	.315 inch	1.90 carat
3.6 mm		.17 carat	8.2 mm	323 inch	2.00 carat
3.7 mm		.18 carat	8.4 mm		2.15 carat
3.8 mm	.150 inch	1/5 carat	8.6 mm	.338 inch	2.25 carat
3.9 mm		.22 carat	8.8 mm	.346 inch	2.50 carat
4.0 mm	.158 inch	.23 carat	9.0 mm	.354 inch	2.65 carat
4.1 mm	.162 inch	1/4 carat	9.2 mm		2.85 carat
4.2 mm		.30 carat	9.4 mm	.370 inch	3.00 carat
4.4 mm	.173 inch	.33 carat	9.6 mm		3.15 carat
4.5 mm		.35 carat	9.8 mm		3.35 carat
4.6 mm	.181 inch	1/3 carat	10.0 mm	.394 inch	3-1/2 carat