Diamonds are weighed in units called carats, the easiest of the 4Cs to determine.
A carat is a unit of measure for diamond weight and is evaluated on a point system. One carat is equivalent to 100 points; a half-carat diamond is 50 points, and so on. One carat also equals 200 milligrams, and 142 carats equal one ounce.
It's also important to note that “carat” should not be confused with “karat,” the unit that measures the purity of gold. The term “carat” is derived from the carob seed, the ancient unit of measure for diamond weight. As technology evolved, jewelers began using mechanical balances and electric scales to measure carat weight accurately. Today, most diamonds are weighed using digital gem scales.
Although diamonds come in many weights, one-carat diamonds are found in nature less often than smaller diamonds and are therefore much more expensive. For this reason, a one-carat diamond costs far more than two half-carat diamonds of the same cut, color and clarity.
When choosing the right carat weight, you must take several factors into account. Remember that any diamond will look bigger when worn on a small hand. And the type of setting can affect a diamond’s appearance.
Interestingly, the largest diamond ever found was the Cullinan Diamond, weighing in at 3,106.75 carats (or one and one-third pounds) and mined from South Africa in 1905. For practical reasons, the Cullinan was cut into nine large diamonds and 96 smaller satellite diamonds. Two of these diamonds of the Cullinan are now part of the British Crown Jewels.