A carat (ct) is the standard unit of measurement used to describe the weight of a diamond. One carat is equal to 200 milligrams (or 0.2 grams). Carat weight is usually measured to three decimal places and rounded to the nearest hundredth.
An important distinction is that the carat weight is not exactly the size of a diamond. They are closely related (a diamond with a higher weight is more likely to be larger), but there are other factors like cut proportions that can affect how large a diamond appears.
The origin of the word carat comes from carob trees in the Mediterranean region. Ancient traders realized that the seeds of carob trees were consistent and uniform in both size and weight so they started using the seeds on scales when weighing diamonds and other gemstones. One of these carob seeds is roughly equivalent to one modern carat.
Carat weight has a significant impact on the price, but this impact is not linear. Larger diamonds are rarer, so prices increase exponentially with carat weight. Their rarity stems from the fact that diamonds are formed deep within the Earth’s crust, where only a select few emerge with the size and quality, often referred to as ‘gem grade’ that is required to be transformed and polished into the brilliant stones that are treasured in fine jewelry. Furthermore, larger stones are even more rare with an estimated one million rough diamonds being mined in order to produce a single one-carat diamond.
As a result of these factors, as the weight of a diamond increases, its price will increase even further. For example, a 0.50 carat diamond will be approximately 3-4 times the price of a 0.25 carat diamond, and a one-carat diamond would be approximately 4-6 times the price of a 0.50 carat diamond.
