Calibrated Size Charts for various types of gemstones set into standard jewellery mountings
Most gemstones are sold in specific calibrated sizes. The idea here is that the stones will fit standard commercial jewellery such as rings, bracelets, necklaces and earrings. However this does not mean that one has to have a specific size. Most jewelers can accomodate an unusual sized diamond and provide a fitting for it.
The main reason that diamonds are sold in specific calibrated sizes is that it is economically easier to produce gemstones that fit into standard settings. Custom made setting involve more labor and therefore a higher cost and expense. This should be kept in mind when buying a loose diamond or loose stones for settings. Having said that, a diamond, or any other gemstone, does not need to be exactly the right size. A professional jeweler can ensure a setting fits by modifying it slightly to accomodate the gemstone. Variations such as .1 imm for under a carat and .2 mm for over a carat can be accommodated easily.
The weights given here are a guide only. They are for diamonds cut to specific proportions. You will find that colored gems are usually cut slightly larger than diamonds. and so will weight a bit more than is shown on the charts below. The density of a gemstone also affects the weight of course with diamonds being the heaviest.
The list is very much a guide and is made available to give one an idea of the type of weights one would have for each setting.