A 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.

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

A large diamond is not necessarily a beautiful diamond! There are a number of factors to consider before purchasing a diamond.