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Understanding Carat Weight

A diamond’s weight is measured in what is known as a ‘carat’, which is a small unit of measurement equal to 200 milligrams. Carat is not a measure of a diamond’s size, since cutting a diamond to different proportions can affect its weight. (NOTE: The word ‘Karat’ is used to express the purity of gold, and is not used in relation to diamonds.) Here is a diagram that shows the relative size of various carat weights in a diamond that is cut to the same proportions:

Note: the diamonds illustrated are not shown actual size.


Although they can be measured when mounted in jewelry, diamonds are most accurately weighed when they are not mounted in a setting. A diamond grading report will tell you the exact carat weight, to the nearest hundredth of a carat, for that particular diamond. Each Carat is divided into 100 parts called 'points.' So a 1-carat diamond has 100 points, a 3/4carat has 75 points, etc. Points in a fraction of one carat are measured within ranges, so that a 3/4-carat diamond may have between .69 and .82 points and still be considered a 3/4-carat.

Here's a table of size and weight ranges showing Carat Fractions and Their Decimal Equivalents:

1/10 = .09 - .11

1/8 = .12 - .13

1/7 = .14 - .15

1/6 = .16 - .17

1/5 = .18 - .22

1/4 = .23 - .28

1/3 = .29 - .36

3/8 = .37 - .44

1/2 = .45 - .58

5/8 = .59 - .68

3/4 = .69 - .82

7/8 = .83 - .94

1.0 = .95 - 1.05


The carat weight of a diamond is an extremely important determining factor in its value. Diamonds are valued on a per-carat basis. For example, a diamond of exceptionally high quality may sell for $20,000 per carat, while one of lesser quality may sell for $1,000 per carat. So, a three-carat stone could be $60,000 or $3,000, depending on its per-carat price. Diamond values also increase disproportionately as the size of the stone increases. In other words, a two-carat stone will not necessarily cost twice per carat than a one-carat stone. It could cost much more, since diamonds are rarer in larger sizes. As you take a stone of a particular cut, clarity and color and move its carat weight to the next price category, you may see quite a large increase in the price per carat. Remember that size isn't everything. When choosing a diamond, all 4Cs must be taken into account. The key is to strike a balance among them, while still working within your budget.


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