Diamond Grading Carat 

The all essential carat weight

Diamonds and other gemstones are weighed using metric carats with one carat weighing about the same as a small paper clip, or 0.2 grams. Just as a dollar is divided into 100 pennies, a carat is divided into 100 points which means that a diamond of 50 points weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other three characteristics of a diamond’s 4Cs: clarity, color, and cut. The majority of diamonds used in fine jewelry weigh one carat or less.

Because even a fraction of a carat can represent a considerable difference in cost when purchasing diamonds, exact precision is crucial. In the diamond industry, weight is measured to a thousandth of a carat and rounded to the nearest hundredth. Each hundredth is called a point (a 0.25 ct. diamond would be called a “twenty-five pointer” or Quarter carat). Diamond weights greater than one carat are expressed in carats and decimals. (For instance, a 1.08 ct. stone would be described as “one point oh eight carats,” or “one oh eight.”)  *GIA Photograph

• What are "magic sizes"?
  Some weights are considered "magic sizes" - half carat, three-quarter carat, and carat. Visually, there's little difference between a 0.99ct. diamond and one that weighs a full carat. But the price differences between the two can be significant.

• How did the carat system start?
  The modern carat system started with the carob seed. Early gem traders used the small, uniform seeds as counterweights in their balance scales. The carat is the same gram weight in every corner of the world.

Carat weight has a great deal of influence on the price of a diamond -- more so than one might imagine at first. Since larger stones are more rare in nature, they are more expensive as well. For instance, one diamond weighing 2 carats will always cost much more than two diamonds of the same quality weighing 1 carat each.

Below is an approximate comparison of the major diamond weights to act as a starting point in your consideration.

Diamond sizes

Carat weight has a great deal of influence on the price of a diamond -- more so than one might imagine at first. Since larger stones are more rare in nature, they are more expensive as well. For instance, one diamond weighing 2 carats will always cost much more than two diamonds of the same quality weighing 1 carat each.

Below is an approximate comparison of the major diamond weights to act as a starting point in your consideration.

Important: Monitors vary widely

Hold an actual dime over the picture of the one above.  If the dime above is actual size, then the diamond sizes in this chart are accurate for your monitor.