A diamond’s weight is measured in units called carats, each equivalent to approximately one fifth of a gram. The word derives from the name for the tiny seeds of the carob tree, which were traditionally use to weigh diamonds in the ancient Middle East due to their uniform round size. A carat is often expressed in points (1/100ths of a carat) so that a half-carat diamond measures 50 points for example. The carat weight of the diamond measures not just the surface or width of the gemstone but the whole dimensions including depth.
All diamonds were formed millions of years ago and display natural characteristics in the form of inclusions, which can block the light. These natural inclusions are like natures fingerprints within the diamonds and no two diamonds are the same. The higher on the scale you go, the less inclusions there are within the diamond, which offers more reflection on the facets and therefore sparkle. Some of the higher graded diamonds in the region of flawless and internally flawless again carry such a premium that you just don’t see them on the market. A good grading to go for is between the SI (slight inclusions) and I1 grading. Lower than this and you would start to see little black dots in the diamond affecting the overall beauty.