Metric conversion chart, about calibrated gemstones.

About Calibrated Gemstones.
Frequently Asked Questions About Gemstone Sizes.
Why use calibrated gemstone sizes in jewelry?
Why isn't the carat weight most important in jewelry design?
Why not define the size of jewelry strictly by gem carat weight?
Why are gemstones calibrated in metric units?
Answer: Economics and to save time.

Calibrated gemstones (not a new concept) came into play long ago due to a gemstones specific gravity or density (a materials weight per its size). Every gemstone varies and has it's own unique specific gravity. In short different materials have different weights such as a block of marble and the same size block of wood.

Lets compare two gemstones. A ruby with a density of 4 and an opal with a density of 2. A Ruby weighs two times as much as an Opal of the same size. Therefore the opal will be twice the size of a ruby at the same weight.

Let's look at a one carat opal and a one carat ruby. We can now see the opal will never fit into the same mounting the ruby is in. The opal, being lighter in weight than the ruby, would be twice the rubies size. We will need a different mounting for each gemstone of the same weight.

1 carat opal/1 carat ruby
visual comparison.
There are many gemstones (over 3000) and all of them vary in weight. Custom metal work is required if carat weight is used to define the size of the piece of jewelry for each gemstone. This would add a great deal of time and cost in producing each piece of jewelry. So gemstones and cast mountings are calibrated to save all of us cost and time.

Why use metric units. See our Gemstone information pages and view some of the gemstones MAJOR SOURCES. You will find many, if not most, gemstone do not come from the United States. We all know that most countries in the world use metric units. Gemstones come from many countries so metric units are used in gemology as well as jewelry. The best we can do is to convert to English units as close as possible.

The conversion chart below will help those of us not accustomed to metric units visualize size.
You can also use our carat conversion charts to estimate many gemstone weights per mm size.

Carat conversion charts for gemstones.
Marquise cut gems, Octagon (emerald) cut chart,
Oval cut chart, Pear shape gems, Round cut gems,
Round diamond carat conversion chart

For more diamond information. Visit our "Four C's diamond grading chart".
Find more gemstone information. Visit our "Gemstone" index.

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