Carat in a diamond is a weight indicator, where 1 carat equals 0.2 grams in weight. The smallest weight in diamonds is called a “point”, which equals 1/100 of a carat. So if a diamond is categorized as a ¾ carat, it weighs between 70 points and 89 points. The ½ carat bracket would weigh 50 points to 69 points.
The term “Carat” originated from the seeds found on the Carob tree. Miraculously, these seeds weigh an exact 0.2 grams, and were used by gem traders for hundreds of years as the most efficient means of determining a gem’s weight and value.
When buying from a diamond dealer, the value of a cut and polished diamond is based on the rough it was cut from. It is essential to understand this concept in order to understand why prices vary when buying a diamond of similar weight, color, clarity but different shape. In most cases, a round diamond is 20%-40% more expensive than any other shape of the same carat, color and clarity. The reason is quite simple. Diamond rough is normally found in 4 types of crystalline shapes: Octahedron, Dodecahedron, Rhombododecahedron and Cube.
In order to cut a round diamond from one of these crystalline shapes, much of the weight would be lost. Many other shapes would salvage more weight from the rough diamond. However, the cost of the rough remains the same. Let’s take a 3 carat rough Octahedron as an example. If we were to create a round brilliant diamond, we would lose roughly 60% of the rough weight, with a final product of a 1.20 carat. Now let’s rewind and re-cut that same 3 carat rough into a princess cut diamond. In most cases when cutting the appropriate shape in respect to the rough diamond, a cutter would lose approximately 40% of the original weight, resulting in a 1.80 carat Princess cut diamond. The cost of both diamonds is the same, and so is the color. The clarity might differ, but let us assume they’re the same as well. Since the cutters and dealers work on a tight schedule with specific percentages, both these diamonds should be very similar in pricing.
This idea applies to a diamond’s overall cut grade as well. A 1 carat with a fair cut grade could be cut down to a 0.90 carat with a better cut grade. In most cases, the pricing would be very similar.