Carat Weight

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Carat weight is the unit of measurement that is used by the jewelry industry to weigh gemstones. One carat is equal to .2 grams or there are five carats in one gram.

Here is a chart which provides an idea of how large a particular weight, well-cut round ruby, emerald or sapphire looks like:


Choosing Ruby Size

Choose A Carat Weight
1/4 1/3 1/2 3/4 1 1
2 3 4 5

As you can see, a 2-carat ruby is not twice as big as a 1-carat one. Also, the price per carat of a 2-carat ruby or other gemstone is significantly more than a 1-carat, assuming both gemstones are of the same quality in all other aspects. The reason for this is simple: A two carat ruby or sapphire is much rarer than a one carat one and thus it is more valuable than a 1-carat ruby or sapphire.

Important Note on Carat Weight among different gemstones
One important point to note is that a 1carat sapphire or ruby doesn’t physically look as big as a 1carat diamond. The reason? Is specific gravity. Ruby and sapphires are much more dense then a 1carat diamond. Look at the chart below for details:

Gemstone Name Specific Gravity Mohs Hardness
Diamond 3.51 10
Emerald 2.63-2.91 7.5-8.0
Ruby 3.96-4.05 9.0
Sapphire 3.96-4.05 9.0

As you can see ruby and sapphire are about 20% more dense then a diamond and when you add in to the fact that they are not cut to exact proportions like diamonds the visual difference is generally close to 30%. So that means a 1carat diamond would look similar to a 1.30ct ruby or sapphire. In other words, the measurements of a 1carat diamond round are 6.5mm and to have a 6.5mm ruby or sapphire you would need to find a stone which is closer to 1.30cts. However, for emeralds, since they have much lower specific gravity than diamonds but are not cut to as exact proportions as diamonds, will generally have the same look as a diamond for a given carat weight. So a 1carat diamond and 1carat emerald will both have measurements which will be approximately 6.5mm.

Furthermore, not all 1carat rubies, sapphire, diamond or emerald will look the same. The main reason is that not all stones are cut the same. Some stones are very shallow (meaning depth proportion is less compared to the length and the width) and thus will have a much bigger face or vice versa. For example, a one carat emerald round will generally have 6.5mm diameter because generally for such stones the depth percentage is close to 70% (or 4.55). However, if a stone is shallow and has depth percentage of 60% (3.9) width, the diameter will be closer to 7mm. The emerald which is shallow will appear 15% larger from the top than the other emerald even though they both weigh the same.


So What Is The Best Carat Weight For Her?

Firstly, the right question should be what measurements are right for her? As we have seen above based on the type of gem and the way its cut, the physical size from the top (or the face up view, also known as the ‘crown’ of the stone in gemology) will vary. Now to evaluate, what measurements are right for her will require one to understand her preferences better. Here are few suggestions:

  • The type of jewelry she currently wears is a great indicator of her likings.
  • Try in covert ways to find out her preferences without her suspecting anything.
  • Ask family members. Ask her sister, mother, cousin or a close friend to understand her likings better.
  • Ring size can be an indicator of the type of ring and the gemstone size to choose. Generally somebody who has very thin fingers and is a ring size 3.5, will not prefer rings with very large gemstones (like a 5carat size sapphire which measures 11mm). However, everybody has different preferences, so this option should be used as a last resort.