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Diamonds - Carat

Carat is the term used to describe the weight of any gemstone, including diamonds. Although the definition of a carat has changed over time, since 1913 the international standard has been 200 milligrams, or 1/5 of a gram. Often, jewellers describe carats in 1/4 increments.

In jewellery pieces with more than one diamond, the carats may be described in terms of total carat weight (TW). This is the combined total weight of all the stones in the piece.

Diamonds can range in size from a fraction of a carat to several carats. Given the rarity of large stones, however, the price increases rapidly with size; therefore, a single 2-carat diamond will cost much more than two 1-carat diamonds. Very large diamonds with good colour and clarity are very rare.

Expect to pay a premium for stones that are above a full carat weight. For example, a .95 carat diamond will cost a bit more than a .90 carat diamond, but a 1-carat diamond will cost significantly more than a .95 carat diamond.

Because round brilliant cuts follow exact standards, you can make a good estimate of the carat weight of the diamond based on the it's diameter. The following chart compares the relative sizes of diamonds and describes how much a round brilliant diamond of a certain size is likely to weigh. This method doesn't work as well for other cuts or shapes, though, since some are thicker or thinner than others; nor does this chart apply to coloured gemstones, which have a different density from diamonds.

.03 carat diamond .05 carat diamond .07 carat diamond 1/10 carat diamond
.03 carat .05 carat .07 carat .10 carat
2.0mm diameter 2.5mm diameter 2.7mm diameter 3.0mm diameter
1/6 carat diamond 1/5 carat diamond 1/4 carat diamond 1/3 carat diamond
.15 carat .20 carat .25 carat .33 carat
3.4mm diameter 3.8mm diameter 4.1mm diameter 4.4mm diameter
3/8 carat diamond 1/2 carat diamond 5/8 carat diamond 3/4 carat diamond
.40 carat .50 carat .65 carat .75 carat
4.8mm diameter 5.2mm diameter 5.6mm diameter 5.9mm diameter
7/8 carat diamond 1 carat diamond 1 1/4 carat diamond 1 1/2 carat diamond
.85 carat 1.00 carat 1.25 carats 1.50 carats
6.2mm diameter 6.5mm diameter 7.0mm diameter 7.4mm diameter
1 3/4 carat diamond 2 carat diamond 2 1/4 carat diamond 2 1/2 carat diamond
1.75 carats 2.00 carats 2.25 carats 2.50 carats
7.8mm diameter 8.2mm diameter 8.6mm diameter 9.0mm diameter
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