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How to Measure Gemstone Carats & Dimensions

Gemstones of all varieties need to be measured by cut, color, clarity and carat weight -- called the 4 C's -- to determine their real market value. A gemstone's dimensions refer to its cut in particular, while carat weight determines its size. A jeweler or gemologist certified by the Gemological Institute of America, or GIA, can weigh a gemstone on a microbalance scale and compare its carat value in accordance with the stone's charted classification. A gemstone's cut -- deep, shallow, fine or ideal -- determines its value based on its ability to refract light through the center or "crown." Symmetry, proportion and facet number also determine cut quality. Accurate cut and carat measurements are especially vital for custom settings.

Instructions

- 1
  Weigh gemstones using a gemstone micro-balance scale to determine its base carat weight. You can also determine a faceted stone's carat weight by measuring the millimeter distance across the top of the stone. Determine each stone's value by using a sizing chart corresponding to the stone's type.
- 2
  Determine each gemstone's cut grade by first identifying the type of the cut. The type of cut can significantly affect the stone's value based on how it can refract light. An ideal cut, for example, will refract light from the center, thus commanding the highest value. A deep or shallow cut, on the other hand, will refract light it from the sides or the bottom.
- 3
  Measure the proportion, symmetry and number of facets respective to each gemstone. A quality cut grade will not only refract light from the center, but will also have an even number of equally-sized facets. Each side must be equal in millimeters. Score the overall cut grade using the GIA scale for cut ranging from 1 (Poor) to 10 (Excellent). Score cabochon, or rounded, facetless stones by symmetry and polish.
- 4
  Select an appropriate setting once cut and carat weight have been graded. Color and clarity is also best determined prior to setting a stone.

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