Carat is the one most people know about, but carat does not refer to the size of the diamond, but the weight!
Carat weight is an essential factor in determining a gemstone's value, with larger diamonds being rarer and thus more expensive. However, it's important to note that carat does not directly correlate with size, as the cut and shape of the stone also play significant roles in how big a diamond appears visually. Carat weight, although a universal term for all gemstones, does not mean that a 1ct diamond and a 1ct sapphire will visually be the same size, due to the varying density of the stones. This is why considering the actual dimensions in millimetres of a stone can provide a more accurate representation of its size than relying solely on carat weight.