The Diamond Guide: Carat

What Is a Carat?

Carat is often mistaken for a measure of size, but it actually refers to weight. One carat is equal to 0.2 grams, which is roughly the same as a small paperclip. While larger carat weights can suggest a bigger diamond, how it looks on the hand also depends on its cut and proportions.


The term itself has an interesting history. Early gem traders used carob seeds as counterweights on balance scales, as they were thought to be fairly consistent in size and weight. Before things were standardised, different regions measured gemstones in different ways, which led to some confusion. It wasn’t until 1913 that the metric carat was formally adopted, giving us the universal system used today.


Carat is one of the four main factors used to assess a diamond, alongside cut, colour, and clarity. It’s also easy to confuse with “karat,” which relates to the purity of gold rather than the weight of a stone. While carat does play a role in a diamond’s value, it’s only part of the picture. How the diamond is cut and how it handles light can make just as much of a difference to how it appears.

How Big is a Carat?

Carat refers to a gemstone’s weight, not its size. Because different stones have different densities, a one-carat diamond won’t always appear the same size as a one-carat sapphire. For example, a round diamond at one carat may measure around 6.4mm in diameter, while a sapphire of the same weight could be slightly smaller.


How large a gemstone looks also depends on its shape, cut, and depth. Two stones with the same carat weight can appear quite different once set in a ring.


It’s worth keeping in mind that every gemstone is unique. Carat weight is just one part of the picture. Proportions and cutting style play just as much of a role in how a piece looks when worn.

How is a Carat Measured?

A carat, equating to 200 milligrams, is the universal unit of weight for diamonds and gemstones. Each carat is meticulously divided into 100 ‘points,’ enabling precise measurements down to the thousandth decimal place. To guarantee absolute accuracy and consistency, expert gemologists employ highly specialised micro-balance scales when determining a diamond’s exact carat weight.

Are Diamond Carat and Diamond Size the Same Thing?

Carat and size aren’t the same thing. Carat is a precise unit that measures a diamond’s weight, not its physical dimensions. It’s easy to assume that a higher carat means a larger-looking stone, but that isn’t always how it works. Looking at carat alone can give a slightly misleading picture.


Different gemstones have different densities, so two stones with the same carat weight can appear quite different in size. Even with diamonds, how the stone is cut has a big impact on how large it looks when worn.


A diamond with poor proportions, for example, may carry extra weight in its depth or have a thicker girdle. That weight isn’t always visible from the top, so a 1.20-carat diamond like this might look no larger than a well-cut 1-carat stone, despite the higher weight and cost.


Understanding this balance helps when choosing a diamond. It’s not just about the number on paper, but how the stone actually looks, feels, and performs in the light.

What Does CTTW Mean?

CTTW, TCW, and TW all stand for ‘Carat Total Weight,’ a measurement that represents the combined weight of all diamonds in a piece of jewellery. This distinction is especially important for jewellery featuring multiple stones, such as diamond bracelets, halo engagement rings, or stud earrings.


For example, when purchasing diamond stud earrings, the CTTW listed refers to the total weight of both earrings together, rather than the weight of each individual stone. If a pair of studs is advertised as 1 CTTW, each earring would typically contain a 0.50-carat diamond. Understanding this terminology helps buyers make informed decisions and ensures clarity when comparing different pieces.

How important is carat weight?

Diamond carat weight plays a crucial role in a buyer’s decision, as it directly influences both the visual impact and the price of a diamond. As one of the 4 C’s—cut, colour, clarity, and carat—it is a key factor in assessing a diamond’s overall value.

Generally, when cut, colour, and clarity are identical, a diamond’s price rises significantly with carat weight since larger diamonds are far rarer. However, carat weight alone doesn’t determine value—two diamonds of the same weight can differ greatly in price based on their cut quality, colour grade, and clarity. This is why an informed balance between all four factors is essential when selecting the perfect diamond.

How does carat weight impact price?

Carat weight has a substantial influence on a diamond’s price, with larger diamonds commanding significantly higher values due to their rarity in nature. This scarcity means diamond pricing isn’t linear—a one-carat diamond will always cost more than two half-carat diamonds of the same quality.

One of the clearest examples of carat’s impact on price comes from what the diamond industry calls ‘magic sizes.’ These are specific weight thresholds—such as ½ carat, ¾ carat, and 1 carat—where the price per carat jumps significantly. Because these sizes are highly sought after, demand pushes prices even higher. For instance, a 0.97-carat diamond and a 1.03-carat diamond with the same cut, colour, and clarity may appear virtually identical, yet the latter will be far more expensive simply because it crosses the coveted one-carat mark.

Is carat the only factor that affects the size and appearance of a diamond?

Carat weight alone doesn’t determine how large a diamond appears. Other crucial factors—such as shape, depth, and symmetry—play a significant role in how big (or small) a diamond looks when set in jewellery.

Elongated shapes like oval, emerald, and marquise tend to appear larger than round diamonds of the same carat weight because they distribute more of their weight across their length rather than in depth. This gives them a more prominent surface area when viewed from above.

Even within the same shape, depth variation can create a noticeable difference in perceived size. For instance, a one-carat pear-shaped diamond with a shallow depth will look significantly larger than a one-carat pear with a deeper cut, as more of its weight is hidden below the surface.

To maximise a diamond’s visual size without increasing carat weight (and cost), check the depth percentage and shape proportions on its certification report. A well-balanced depth-to-table ratio ensures a diamond looks as large as possible while maintaining brilliance and fire.

Any tips on how to make a diamond look bigger?

Halo Settings: Opting for a halo setting can dramatically enhance the perceived size of your centre stone. By encircling the main diamond with smaller accent diamonds, you can create a striking effect that amplifies its brilliance and size appearance. This shimmering border draws the eye outward, making the centre diamond look even more prominent.

Delicate Bands: The thickness of the band can greatly influence the perceived size of the diamond. A thinner, more delicate band allows the centre stone to take the spotlight, making it appear larger. On the other hand, a thick band can overshadow the diamond, making it seem smaller in comparison.

Consider a Lab-Grown Diamond: Lab-created diamonds offer the opportunity to purchase a higher carat weight at a more affordable price compared to natural diamonds. These diamonds are optically, chemically, and physically identical to mined diamonds, offering the same stunning brilliance but at a fraction of the cost. This is an ideal option for those wanting a larger statement piece without the hefty price tag.

Regular Cleaning: Keep your diamond sparkling to ensure it shines brightly and looks its best. A well-maintained, clean ring will always appear more impressive and larger than a dirty, dull one. Regular cleaning not only enhances its size appearance but also keeps your stone looking as beautiful as the day you first set eyes on it.

What is the average carat size for engagement rings?

The average carat weight for engagement rings typically falls around 1.5 carats. Engagement rings featuring lab-grown diamonds tend to be slightly larger than their natural counterparts.

How much is a 1-carat diamond ring?

The average cost of a 1-carat natural diamond ring is £‌7,300.00. The average cost of a 1-carat lab diamond ring is £‌3,400.00

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