Maybe you're a jeweler at a local jewelry store and need to measure a loose gemstone. Or perhaps you're looking at making jewelry and need to fit a gemstone to a certain ring or necklace. There are many instances where you may find yourself needing to know how to measure a gemstone, either by weight or size. There are a numebr of techniques to help you properly measure a gemstone either for jewelry use, appraisal or personal knowledge.
Measure the diameter of a gemstone by using a caliper, either a manual one or a high quality, electronic calibrated one. This will tell you the diameter of a the gemstone, which is essential if using the gemstone in a jewelry setting or for a specific use.
Determine the carat weight of a gem. This is one way to measure a gemstone to determine its worth, and can be done with a special, highly sensitive gemstone scale. A carat weighs .2 grams (or in U.S. measurements, .007 ounces), so it is important to have a special gem scale in order to properly determine the carat measurements of a gemstone.
Estimate the size of a given gemstone by using a stone gauge or hole gauge. These are rulers or templates with varying sizes of holes in which you can pass a gemstone through to estimate its approximate diameter and size. This does not, however, help you determine the carat weight of a gemstone, but can be helpful for a jeweler that is trying to fit a gemstone for a particular setting.
Invest in a Leveridge gauge, which can help you measure gemstones with extreme accuracy. Leveridge gauges appear like a scale that you would see at a supermarket for produce, but have a caliper on the top, so you can not only measure length and width, but weight as well. This can be used for measuring gemstones in or out of a jewelry setting.