Weight Length Conversions

Weight Length Conversions

Well you will find in the gemstone world that the Metric and American measuring systems are pretty intermixed. So you will need to know both systems on some occasions.

Weight Conversions: (Avoirdupois) 1 carat = 100 points (you will hear points used a lot in diamonds)
5 carats = 1 gram
141.7 carats = 1 ounze (Av.) = 28.349 grams
2267.9 carats = 1 pound (Av.) = 453.6 grams
5000 carats = 1 kilo = 2.20 pounds (Av.)
1 grain = 1/4 carat
1 momme = 18 3/4 carats (used in pearls mostly)
1 carat = 200 milligrams

Measure Conversions: (Metric to U.S. Inches) 1 micron = 1/1000 mm = 1/25,400 inch
1mm = 1000 microns = 1/25 inch
10mm = 1 centimeter = .39 inch
25.4001 = 1 inch = 2.54 centimeters

Here are a few interesting facts you may not know. Before 1913 a “carat weight” varied depending on the country of origin. If you are thinking of buying estate jewelry or gems, be aware that a carat weight listed on an old certificate may not be the same weight of a modern carat. Check it.

Since 1913 a carat (metric carat) have been generally agreed to be 1/5 of a gram or 200 milligrams… and this is the weight used in most modern trade today. Hope this makes it easier for you to figure these measurements out.

Gram Faceting Archive of Information
This edited version of an article by the late Jeff Graham is part of a special archived informational series from Gram Faceting. Used with permission.