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Gemstone Carat Weight Estimation Calculator

This calculator requires the use of Javascript enabled and capable browsers. This script calculates weight conversions between grams of weight and carats, points, kilograms and milligrams. Carats, abbreviated "ct." and spelled with a "c", is a measure of weight used for gemstones. The carat weight was standardized in the 20th century. The United States officially adopted the metric carat in 1913. One carat = .2 grams or 200 milligrams, equal to 1/5 of a gram. Stones are measured to the nearest hundredth of a carat. A hundreth of a carat is also called a point. Thus a .10 carat stone can be called either 10 points, or 1/10 of a carat. Small stones like .05, and .10ct are most often referred to by point designations. The spelling of karat with a "K" is a measure of the purity of a gold alloy, as opposed to stones. A one carat round diamond of average proportions is approximately 6.5mm in diameter. Be aware that this unique relationship of weight and size is different for each family of stones. For example ruby and sapphire gems are both heavier than a diamond; technically, they have a higher specific gravity, so a 1 carat ruby or sapphire is smaller in size than a one carat diamond. However, I never met a carat I didn't like!

Select the particular stone and cut. Enter the values and click on Calculate.

Required Data Entry
Girdle Length (mm)
Girdle Width (mm)
Depth (mm)
Avg. Specific Gravity

Calculated Results
Carats Value
Updated 8.12.11

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