When it comes to diamonds, one of the first questions people ask is the weight of the diamond, or carat. The carat is one of the most important factors affecting the appearance and price of a diamond. I’ll tell you a little bit about what exactly a carat is and how it came to be the unit of measurement in the diamond trade.

The carat (ct) is a unit of weight for diamonds and other precious stones. 1 carat weighs exactly 200 milligrams, or 0.2 grams. Although the carat is related to the weight of the stone, it also has a significant effect on the visual size of the stone. The higher the number of carats, the heavier and visually larger the stone.

Where did the word “carat” come from?

The word ‘carat’ comes from ancient trade practices. In the old days, merchants used carob tree seeds to measure the weight of precious stones, as these seeds were uniform in weight. As the carob seeds were quite accurate, they were also used to measure the weight of precious stones, and this unit of measurement remained valid in later times. Eventually, the spindle was standardised into the modern unit of measurement used around the world.

Effect of spindle size on diamond size

The number of carats has a direct impact on the size of the diamond, although the cut and shape of the diamond can also affect the visual size. The following figure shows the approximate dimensions of a round brilliant cut diamond at different carats:

How does the shape of a diamond affect its visual size?

It’s important to remember that a diamond with the same carat can look different sizes depending on its shape and cut. For example:

• Oval cut: an oval diamond may visually appear larger than a round cut of the same carat, as its shape covers more surface area.
• Emerald or radiant cut: these cuts tend to be slightly longer and shallower, which can also make the stone look visually larger.

How does the carat affect the price?

As the carat increases, the price of the stone increases exponentially. For example, while a 0.5 carat diamond may cost significantly less than a 1.0 carat diamond, a 4.0 carat stone that is eight times larger is not necessarily eight times more expensive – but much more, as there are fewer diamonds with higher quality. In addition, the colour, clarity and cut of the stone also affect the price.

The impact of the carat on ring design

The larger the carat of a diamond, the higher the stone rises in relation to the ring. This is a design necessity, as a larger stone requires a larger and more durable mounting. Larger stones are more visually striking and elegant, and require carefully considered mounting solutions.