Carat Weight

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Carat is the unit of measurement of the weight of a diamond. In terms of grams, a carat is equivalent to only 0.2 grams.

The term "carat" originates from The Middle East where around 500BC they used seeds from a carob tree to measure the weight of diamonds, as it was thought that carob seeds all had identical weights. Interestingly enough, in recent times, this theory has been dis-provenExternal Link .

In 1913, the carat measurement was introduced in the United States and is now the standard across the world.

Carats and Points

A carat consists of 100 points. Therefore, a 0.50 carat diamond is equivalent to 50 points. It is also not uncommon to hear diamond merchants refer to smaller diamonds in terms of points. For example, a diamond weighing 10 points may be called a "10 pointer".

Measuring Carat Weight

Measuring carat weight is a simple and objective procedure using a specialised gem scale. An example of such a scale can be seen at DendriticsExternal Link.

Relationship to Diameter

It is important to note that a diamond weighing two carats will not have twice the size of a diamond weighing one carat.

Diamondring.comExternal Link shows that whilst a 0.5 carat diamond should have an approximate diameter of 5.2mm, a 1 carat diamond will have an approximate diameter of 6.5mm.

Relationship to Cut and Spread

Sun JewelryExternal Link states:

It is very important that one does not relate the numerical values of carat weight as a judgment of a diamonds actual diameter size.

This is due to the fact that a cutter may sacrifice a good cut in order to achieve a higher carat weight. This can be done through cutting a thicker girdle or by making the overall depth bigger.

Sun Jewelry then goes on to state that:

Undersize inferior cut diamonds are abundant in all size ranges and are commonly sold with GIA, EGL and IGI and other diamond quality reports. Because GIA, EGL, IGI and other gemological laboratories do not assign a overall cut grade, it is up to the individual to know a diamonds depth percentage, table percentage, girdle thickness, culet, polish, symmetry and more.

Relationship to Price

As larger diamonds are more rare, there will not be a linear increase in price between carat weights. This means that a two carat diamond will cost more than double a one carat diamond.

In addition, as weights reach certain "milestones", a premium is generally added. For example, one may pay a premium for a one carat diamond over a 0.99ct carat diamond. Fred CuellarExternal Link states that to overcome this problem, one may "buy shy" to save money.

Choosing The Best Carat Weight

Blue NileExternal Link has a guide to choosing the best carat weight, along with an interactive pictorial of various carat weights.