Carat is a unit of weight, not purely “size” as many people misconceive. The metric carat (0.2 grams or 200 milligrams) is the standard unit used to weigh all species of gemstone, not just diamonds. The term derives from the Carob seed as the seeds from this tree are remarkably consistent in weight so were used by historical gem traders.

The carat is divided into a hundred “points” – just like pennies in the pound – so a diamond that weighs three-quarters-of-a-carat is can also be expressed as “seventy-five points”.


All other factors being equal (colour, clarity, cut-grades etc.), the greater the carat-weight of the diamond, the greater the price.
Although we started by saying that carat is not a measurement of size, there are a few things to consider when purchasing: – the round brilliant cut diamond – the cut that is fashioned to the most exacting measurements (and the only shape assessed for its “cut grade”) – should be within certain tolerances for its face-up diameter in relation to its weight. For example, a well-proportioned 0.75ct diamond should have a diameter of approx. 5.9mm. If a round brilliant diamond weights 0.90ct but also measures 5.9mm in diameter, then the diamond is too deep – this will affect how it returns light to the viewer and it also conceals “hidden weight” which will not be appreciated in the face-up view.

This is not so much a concern when shopping for fancy-shapes – oval, rectangular and square cuts etc. – as there are more proportion variations found in these shapes and people have their own preferences for what they feel is aesthetically pleasing…. Beauty truly is in the eye of the beholder!

If you have any queries on carat, or on gemstones in general, please do not hesitate to contact Finecraft. We would be delighted to hear from you.