Carat: Diamond Weight

Learn how carat weight impacts diamond price, a smart tip to help you pick a carat weight, and what common industry terms mean.

What is TCW? What are points? And what are grains?

“Carat” is a measure of weight, not visual size.  One carat is equal to 200 milligrams.

The weight of smaller diamonds is often expressed as points, not carats. One carat is equal to 100 points. Thus, for example, a 10-point diamond has the weight of 0.1 carats.

A ring with a TCW of 1 carat has a total carat weight of 1 carat, so there may be several diamonds on the ring and all together their combined weight is 1 carat.

The word “carat” originates from the Greek word kerátion, which means carob beans, which were known in the ancient world for uniformity of their size and weight and were used as a measure of weight for different objects, including gemstones. In the Far East instead of carob beans, jewelers used rice grains to determine the weight of gemstones. You may occasionally hear some jewelers referring to a 1-carat diamond a “four grainer,” because in the past 1 carat was equal to four grains of rice.

If everything else is equal, shouldn't a smaller diamond save me money?

Not always.

Diamond prices typically increase at a higher rate from one weight / price bracket to the next. For example, price per carat for diamonds in the size bracket 1.00–1.49 carats could be $8,000, while price per carat in the bracket 1.49–1.99 carats can jump to $11,000.

To maximize the size of the purchased diamond without having to pay a higher price per carat, it is smarter to buy diamonds with the size towards the higher end of a chosen price bracket.  For example, buy a diamond the size of 1.48, rather than 1.51.  The 1.48 carat diamond would be priced at 1.48 x $8,000 = $11,840 while 1.51 carat diamond would be priced at $11,000 per carat and thus would have the value of 1.51 x $11,000 = $16,600, that is $5,000 more for just 0.02 additional carats.

How does carat weight impact diamond prices?

While carat weight is not the only factor in a diamond's price, it is a major piece of the formula--literally.  A regression analysis of diamonds from one popular retailer showed only small price steps for changes in clarity, color, and cut grades, while carat weight changes caused much larger shifts in price.

Side-by-side diamond price comparisons of similar diamonds with varying carat weight show how heavily carat weight can figure into the equation. 

One reason for the large impact of carat weight is Mother Nature.  Finding rough diamonds is increasingly rare with size: for every million pieces of rough material only one piece on average is large enough to produce a 1-carat finished diamond.

A second reason for carat weight's large impact on price is the cutting process.  During the cutting process, a diamond typically loses 40% to 60% of its original rough diamond size. As carat weight gets larger, the value of the diamond stone increases disproportionately.