Diamond Carat Measurement

A diamond carat is a measurement used to signify the weight of the diamond. It is the most precise of the four C's. Diamonds are weighed in metric carats. One carat equals 1/5 gram or approximately 0.007 ounces. It takes a little over 142 carats to equal 1 ounce. Every carat is divided into 100 points. Therefore, a 50-point diamond is also called a ½ carat. Diamond weight is so precise that polished diamonds are weighed to a thousandth of a carat and then rounded off to the nearest hundredth (point). Diamonds weighing less than 20 points are often called melee. Another term often used is grain or grainer.
A grain equals one-quarter (0.25) of a carat. For example, a 75-point diamond would be called in the trade a three grainer and a one-carat stone may be called a four grainer. Loose stones are weighed directly on a scale but mounted stones can only be estimated by plugging their measurements into a mathematical equation. Another quick way of estimating mounted round diamonds is by measuring the diameter of the diamond and comparing it to a size chart.
diamond cut

Magic Sizes

Since the price of diamonds is based upon rarity, the larger the stone the rarer the diamond and the higher the price per carat. A one-carat stone is much rarer than two half-carat stones, and is therefore considerably more expensive.
Magic size also plays a significant role in pricing diamonds. People tend to prefer a one-carat diamond over a 0.99- carat diamond. For this reason alone a 1.00ct diamond is worth much more than a 99-point diamond. Even the most experienced diamond dealer cannot tell the difference without a diamond scale. Could you visualize less than one fourteen-thousandth of an ounce? And yet, people are willing to pay hundreds, sometimes thousands, of dollars for this minute difference in engagement & anniversary diamond rings.

Carat Weight Name
18ct-22ct points or fifths
23ct-29ct points or quarters
30ct-39ct points or thirds
40ct-49ct points; diamonds weighing between 0.46ct and 0.49ct are often called light halves.
50ct-69ct points or halves
70ct-89ct points (three grainers) or three-quarters
90ct-99ct points or 90 pointers
1.00ct-1.49ct carats or spoken four grainers
1.50ct-1.99ct carats or six grainers
2.00ct-2.99ct carats or eight grainers
3.00ct-3.99ct carats
4.00ct-4.99ct carats
5.00ct carats
fetch 5-10% premiums over straight sizes.
0.60ct-0.69ct, 0.80ct-0.89ct, 0.95ct-0.99ct, 1.20ct-1.49ct, 2.50ct-299ct, 3.50ct-3.99ct, 4.50ct-4.99ct
Remember: A large diamond is not necessarily a beautiful diamond! There are a number of factors to consider before purchasing a diamond.
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