4C's - Carat
Diamond carat weight is the measurement of how much a diamond weighs. A metric "carat" is defined as 200 milligrams.
Each carat can be subdivided into 100 'points.' This allows very precise measurements to the hundredth decimal place. A jeweller may describe the weight of a diamond below one carat by its 'points' alone. For instance, the jeweller may refer to a diamond that weighs 0.25 carats as a 'twenty-five pointer'. Diamond weights greater than one carat are expressed in carats and decimals. A 1.08 carat stone would be described as 'one point oh eight carats'.
All else being equal, the diamond price increases with carat weight, because larger diamonds are rarer and therefore, more desirable. But two diamonds of equal carat weight can have very different values (and prices) depending on three other factors of the 4Cs (Cut, Colour and Clarity).
When buying a diamond, it is important to remember that a diamond's value is determined using all of the 4Cs, not just it's carat weight.
When purchasing diamonds, carat weight is the most intuitive of the 4Cs – you expect a larger diamond to be worth more. For more information, take a look at the video below.