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Frequently Asked Questions (FAQ) / Calibrated Gemstones & Size Tolerance

I need a 7 mm x 5 mm gemstone for a standard setting. How much can gems vary in size and still fit standard calibrated mountings?

Calibrated Pear Shape Tsavorite Garnet As a general rule, gems weighing less than 1 carat can be within 0.2 mm of the calibrated size in order to fit a standard calibrated jewelry mounting or setting. This size variance calculation is only a guide and is based on the average size-to-weight ratio of a gemstone cut to standard proportions.

For gems weighing over one carat, typically a difference of 0.3 mm (+ or -) can be accommodated and sometimes more. Round stones allow for greater variance; in fact, it is usually possible to mount a round stone of any size in the closest standard setting. We recommend finding your replacement side stone or center stone through our calibrated gemstone page.

Do keep in mind, that a good jeweler can adjust rings and mountings to fit just about any gemstone that is reasonably close in size to that required; this applies for calibrated commercial jewelry in standard sizes, as well as custom jewelry featuring gemstones cut to exact size with unusual measurements. For example, peg head mountings can often give or take 0.5 mm. In addition, many jewelry designs feature interchangeable heads, which means your jeweler may be able to completely swap out the head and set a gemstone of your choice in any size or shape. If it is not a peg head mounting, jewelers can usually tighten or spread the prongs, and they can even add more material to the prongs and/or mounting to accommodate even more variance. For halo or bezel mountings, jewelers may be able to pinch, mould or spread material depending on the malleability of the material your gemstones are set in.

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  • First Published: February-20-2006
  • Last Updated: September-12-2017
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Size and Weight

Gems are always measured in Millimeter (mm)

Dimensions are given as;
length x width x depth,
except for round stones which are;
diameter x depth

Select gems by size, not by weight!
Gem varieties vary in density, so carat weight is not a good indication of size

Note: 1ct = 0.2g

Size Comparison Chart