Understanding Diamond Carat: What Every Buyer Should Know

What is a Diamond Carat?

Definition of Carat

A carat is a unit of weight used to measure diamonds and other gemstones. One carat equals 200 milligrams, or 0.2 grams. Though this may seem small, even slight variations in carat weight can significantly impact a diamond’s price and appearance. The term "carat" comes from the carob seed, historically used by gem traders as a reference for measuring gemstones. In 1907, the carat was standardized to ensure consistency in the global gem trade.

How Diamond Carat is Measured

Carat weight is measured with extreme precision, often to the hundredth decimal place (e.g., 1.05 carats). Jewelers use specialized scales to determine a diamond's exact carat weight, and even small differences — such as 0.98 carats versus 1.00 carats — can lead to noticeable price variations due to the carat milestone effect.

How Big is a Carat?

A carat refers to weight, not size. For example, a one-carat round diamond typically measures around 6.4mm in diameter, while a one-carat round sapphire, which is denser, might measure only 6.0mm. The size appearance of a carat can also depend on the gemstone's shape, cut, and depth.

For instance, a shallow-cut diamond may have a larger surface area (or face-up appearance), making it look bigger than a deeper-cut diamond of the same carat weight. This is why two diamonds of the same carat weight can appear different in size to the naked eye.

A common illustration of size comparisons shows how round diamonds appear at increasing carat weights. This helps buyers visualize the relationship between carat weight and the size they might expect, though it's essential to remember that each gemstone is unique.

Diamond Carat vs. Diamond Size: What’s the Difference?

Carat Weight vs. Visual Size

Carat weight refers to how much a diamond weighs, while the size relates to its physical dimensions. For example, a one-carat round diamond may appear smaller than a one-carat oval or marquise diamond due to differences in their surface areas. Shape and cut also heavily influence how big a diamond looks. For example, a well-cut diamond with ideal proportions will reflect light more effectively, making it appear larger and more brilliant than a poorly cut diamond with the same carat weight.

Why Shape and Cut Matter

The shape of the diamond significantly impacts its visual size. Round, oval, pear, and cushion cuts all handle light differently, and each shape offers a unique look. Cut quality plays a huge role as well. A diamond with excellent cut proportions may look larger and sparkle more brilliantly than a poorly cut diamond of the same carat weight.

In other words, carat weight alone doesn’t determine how big a diamond will look — cut and shape are just as important.

Is Carat the Only Factor That Affects the Size Appearance of a Diamond?

No, carat weight is not the only factor that affects the size appearance of a diamond. A diamond’s shape, depth, and symmetry also play critical roles in how big or small a diamond appears.

Elongated Shapes Appear Larger

Elongated shapes, such as oval, emerald, and marquise cuts, often appear larger than round diamonds of the same carat weight. This is because elongated shapes distribute more of their weight along their length, giving them a more substantial surface area and a more prominent visual presence.

Depth Affects Size Appearance

The depth of a diamond also influences how large it looks. For example, a shallow-cut diamond will have a broader surface area, making it look bigger than a deep-cut diamond of the same carat weight. A one-carat pear-shaped diamond with a shallow depth will seem larger than a one-carat pear with a deep depth.

Both depth and shape are factors listed on a diamond’s official certification report. If you're trying to maximize the size appearance without increasing carat weight (and cost), pay attention to these details when selecting your diamond.

How Important is Diamond Carat?

Carat weight is often a significant factor for customers, as it directly influences the value of the diamond. As one of the 4 Cs (cut, color, clarity, and carat), carat weight is crucial in determining both the price and desirability of a diamond. Larger diamonds are rarer, and their scarcity drives up the price.

However, two diamonds with the same carat weight can vary greatly in price if their cut, color, or clarity differs. For example, a poorly cut 2-carat diamond may be less valuable than a well-cut 1.5-carat diamond with excellent clarity and color. This is why it's essential to consider all 4 Cs together to ensure you're getting a diamond that not only weighs more but also looks stunning.

How Diamond Carat Impacts Price

Carat weight has one of the most significant impacts on a diamond's price. Larger diamonds are more valuable because they are rarer in nature. As a result, diamond pricing is not linear. For instance, a 1-carat diamond typically costs much more than two 0.50-carat diamonds of the same quality.

The diamond industry uses "magic sizes" to describe certain carat weight thresholds where prices increase dramatically, such as at 0.50, 0.75, and 1.00 carats. For example, a diamond weighing 0.97 carats may be priced significantly lower than one weighing 1.03 carats, even though the visual difference between the two is minimal. The reason is that the second diamond surpasses the "magic" one-carat threshold, driving up demand and, consequently, the price.

More Tips on How to Make a Diamond Look Bigger

If you're looking for ways to enhance the size appearance of your diamond, here are a few strategies to consider:

Halo Settings: Choose a halo setting, which features smaller diamonds surrounding the center stone. This setting creates a shimmering frame around the main diamond, making it appear larger and more brilliant.

Delicate Bands: A thinner band can also make your diamond appear larger. If the band is too thick, it draws attention away from the center stone, making the diamond look relatively smaller by comparison. A delicate band, on the other hand, highlights the stone’s size.

Consider a Lab-Created Diamond: With lab-created diamonds, you can get a larger carat weight for a lower price compared to natural diamonds. Lab diamonds are optically, chemically, and physically the same as natural diamonds, making them an excellent option for those who want to make a big statement at a more accessible price point. Check out our Lab Grown Diamond Guide to learn more.

Regular Cleaning: to maintain the sparkle and brilliance of your diamond, regular cleaning is essential. A dirty or dull diamond can appear smaller and less impressive. Keeping your ring clean will ensure that your diamond shines as brightly as possible, enhancing its overall size appearance.

What Does CTTW Mean?

When shopping for diamond jewelry, you may encounter terms like CTTW, TCW, or TW. These abbreviations stand for "Carat Total Weight," which refers to the combined carat weight of all the diamonds in a piece of jewelry. For instance, if you’re purchasing diamond stud earrings with a total carat weight of 1.00 CTTW, it means the total combined weight of both earrings' diamonds is 1 carat, not that each earring contains a 1-carat diamond.

CTTW is commonly used for jewelry pieces that contain more than one diamond, such as earrings, bracelets, or necklaces.