Understanding Diamond Carat

For the last of  Secrète Fine Jewelry’s blog series on the 4Cs (including colorclarity, and cut), we’re going to get in depth about carat weight.

Carat is the unit of measure for diamond weight. It should not be confused with karat (with a K), which is a unit of purity in gold. A carat is 0.20 grams. Originally, diamond dealers used carob seeds as counterweights on scales, and the name carat actually originates with carob (source- Oxford Dictionaries).

Fractions of a carat are expressed in decimals, called points. For example, diamond that weighs half of a carat can be referred to as a “50 pointer” or a diamond that weighs one and three quarter carats will be written as 1.75.


Secrète custom-designed this engagement ring for a cool young Washington, DC couple featuring an 85-point princess cut center diamond. The side diamonds and pave infinity-inspired shank add to the total carat weight. This ring also features all recycled diamonds for this ethical engagement couple, and an extra-white alloy of 14k white gold which never needs rhodium plating. 

It can be useful to remember that carat is a weight, not a distance, especially when choosing a diamond for an engagement ring or other jewelry. What this means is that our perception of the size of a diamond is based on its measurements when looking at it from the top. Weight and size correlate, but not exactly. Some diamonds are cut deep and “carry their weight in the belly” so to speak, while others are shallow and show off more in the face-- obviously, however, a razor-thin slice of a diamond will look big, but not pretty, so refer to our blog about cut for more about these proportions.

It’s easiest to understand carat as a weight, not a distance, with example. Take, for example, the two stones described in the certificates below. Both weigh exactly 1.00ct. Both are good cut, good symmetry. Both are round brilliants. Both are GIA certified. One measures 5.93mm across, and the other measures 6.67mm across. That over 0.7mm difference; while fractions of millimeters may not seem significant, that’s a big difference in the way a diamond looks. At Secrète Fine Jewelry, our diamond experts will help you find a diamond that looks big on your ring finger, not just on paper.

Two diamonds of the same carat weight and cut grade can be different sizes.
On the left, a 1.00ct GIA certified round brilliant diamond with good cut and symmetry measures 5.93mm across. On the right, a different 1.00ct GIA certified round brilliant diamond with good cut and symmetry measures 6.67mm across. Typically, 1.00ct diamonds are around 6.5mm, but carat is a weight, not a distance.

Another factor to consider with carat weight is pricing. Diamond wholesale pricing involves all of the 4Cs, but the price per carat jumps in increments: for example, the price per carat a particular color and clarity of diamond that weighs 0.70-0.99ct is lower than the price per carat for the same color and clarity in 1.00-1.49ct, and the price rises more the bigger you go, because, obviously, bigger diamonds are more rare. This means that a 0.98ct diamond is priced at a lower rate than a 1.01ct diamond, because it’s just under the incremental limit. Skilled jewelers, like the team at Secrète, will help you get the most for your money, finding a 0.98ct diamond that measures big face-up, at a better price than the identical 1.01ct counterpart.


At Secrète Fine Jewelry, our engagement ring clients can try a wide range of shapes and sizes to get a feel for how a stone really looks on their hand. This hands-on trial process is one of the best ways to learn about the right carat size for your design. 

If this sounds complicated, don’t worry too much about the details. The simple version is this: sometimes going just under the round numbers of carat weight can help you save a lot of money without necessarily having to sacrifice the appearance of size.

Finally, the old axiom is true: size isn’t everything. A gigantic, dingy, M color, shattered-looking, I3 diamond is not better than a more reasonably sized near-white eye-clean diamond. It’s just not. At the same time, a microscopically flawless, absolutely colorless, teeny tiny diamond is… underwhelming. Find a jeweler you trust to work within your budget, whatever it is, to find the sweet spot for your custom engagement ring. 

To meet with one of our team about your custom engagement ring at either of our locations-- DuPont Circle in Washington, DC, or Wildwood Shopping Center in Bethesda, MD-- contact us today!