Carat is the easiest of the 4Cs to understand and evaluate, as it is not at all subjective. All you do is put the stone on a scale and determine out how much it weighs. A carat equals one-fifth of a gram (or 200 milligrams)—the same weight as a dose of aspirin. A carat is expressed in hundredths, each hundredth equaling a point—the same way a dollar is broken down into pennies—so a 0.50 carat diamond equals fifty points or a half-carat in this case.

When assessing a diamond’s carat, it’s important to remember that diamonds can weigh the same amount but look very different size-wise. So, carat is not the only quality to base your purchase on!

As seen in the examples above, a shallow cut diamond viewed from the top will look larger than both the proportionate and deep cut diamonds. However, the proportionately cut diamond will return light the best, meaning it will have more sparkle!

One aspect of this weight/size discrepancy is the shape (or the outline you see when the diamond is facing top up – heart, round, oval, square, etc.) of the diamond – Certain shapes will appear to be larger than others, regardless of a matching carat weight. For example, a 1.00-carat diamond measures an average of 6.5 mm if round, 5.5 x 5.5 mm if princess cut (square), or 10 x 4.75 mm if marquise (almond shaped).

Another factor to be aware of is how the diamond is cut (not just the gem’s shape but the entire 3-dimensions of the diamond, its sides, top, facets, etc.) If a diamond is cut shallow, its top (length-by-width) measurement will be larger than average, and if it is cut deep, it will measure smaller than average. This change in depth will also change the look and light return of the diamond – so be sure to compare diamonds side by side, so you can see the differences.

The size of a diamond and its carat weight are closely intertwined when it comes to price. Diamonds are priced based on a cost-per-carat rate, which is determined by the size of the diamond. The truth of the matter is that the larger a diamond, the greater the cost per carat. There are two reasons for this: 1) Larger diamonds are rarer, and 2) Cutting a larger diamond may result in a greater loss of this rare material.

Diamonds are priced in a range of carat weight increments, usually in half-carats, though the lower the weight, the smaller the increments. For instance, a diamond that weighs .99 carat will have a lower per-carat price than a 1.1-carat diamond. The price difference can be used to your advantage, though, as the overall look of a .99-carat diamond and a 1.1-carat diamond may not be as great as the variance in cost. But if the person who is going to wear the diamond puts more weight (pun intended) on being able to say she has a diamond that is more than one carat, you may just have to go for it, despite the cost deferential.

Diamonds being weighed on a scale.

When considering the carat weight of a diamond, also take into account the size of the person who will be wearing it, the design of the piece, and how important carat is on your priority list. For engagement rings, a smaller stone will look larger on a more petite hand (lucky me!). Fitting a 3-carat diamond with side stones on a size-4 ring (a very small size) may not look as you’d expect or even be physically possible. Just as trying to copy a ring you found in a magazine that shows a 5-carat center stone is not going to look the same if you have a 1-carat center stone. There are some styles, though, like rings with a center stone and a halo of smaller diamonds around it (often called a diamond surround), that can give you more sparkle for fewer carats.

Just some things to keep in mind when determining your carat wish list…!

Bye for now,
Alicia Gardner Kozikowski, G.G.



Still thinking but who do I get a diamond from, the cuts are confusing and how do I know if I’m getting a good deal!?! H+G’s four part series on diamond buying can help! Read on: Buying Diamonds 101: Part I – An Introduction, Buying Diamonds 101: PartII – What You Want to Buy, Buying Diamonds 101 Part III – What You Are Buying, Buying Diamonds 101: Part IV: Who To Buy From