Contrary to popular understanding, a diamonds carat measurement refers to its weight as opposed to its physical size. Carat weight is just one of the 4C’s that are considered when grading the quality of a diamond, the others being its clarity, colour and cut. Different diamond shapes and cuts have different carat weight. At Harper Tait we select a stone for its overall quality prioritising beauty and fire over its physical size.
Although there are a number of other contributing factors that affect the appearance of a diamond, such as cut and shape, you can generally expect the stone to appear larger as the carat weight increases.
A metric carat is equal to 0.2 grams or 0.007 of an ounce. One carat is divided into 100 points. Diamonds are weighed to one-thousandth of a carat and then rounded up to the nearest point, expressed as carats and decimals (e.g. 1.05 carats) or points (e.g. 75 points). A fraction of a carat can affect the price of a diamond by hundreds or thousands of pounds, however, it should be remembered that this is a measure of rarity as opposed to just quantity. Large diamonds are rarer than small diamonds; that is why they are more valuable, not just because they are bigger. That is why a two-carat diamond will be worth more than twice as much as a one-carat stone.
There are also ‘magic numbers’ where the price shoots up dramatically. A one-carat diamond will cost significantly more than a 99 point one, even though they are almost indistinguishable regarding size and appearance. 50 points (half a carat) and 75 points (three-quarters of a carat) are similar symbolic thresholds.
While the four C’s are the universal measures of a diamond’s objective value, we encourage our clients to look beyond these and to choose a diamond that is right for them. However, understanding this grading system is the only way to know how the value of a diamond is arrived at, and as such is an essential part of the buying process.