The Diamond Guide: Carat

What Is a Carat?

Many people mistakenly believe that carat refers to a diamond’s physical size, but in reality, it is a measurement of weight. One carat is equal to 0.2 grams—roughly the weight of a paperclip.


To truly grasp what carat represents, it helps to understand its origins. The term dates back to early gem traders, who used carob seeds as natural, uniform counterweights on balance scales. Before standardisation, different regions used varying systems to measure gemstones, leading to inconsistencies in valuation. It wasn’t until 1913 that the modern metric carat was officially adopted, ensuring that one carat now holds the same weight worldwide.


As one of the four key factors that determine a diamond’s quality and value, carat is often confused with ‘karat,’ which refers to the purity of gold. While carat measures weight, it does not always directly translate to size, as a diamond’s cut and proportions also play a crucial role in its overall appearance.

How Big is a Carat?

Carat refers to a gemstone’s weight, not its size. Due to differences in density, a one-carat round diamond may measure approximately 6.4mm in diameter, while a one-carat round sapphire might be closer to 6.0mm. Factors such as shape, cut, and depth significantly influence how large a gemstone appears.


It is important to remember that every gemstone is unique, and carat weight alone does not determine perceived size—proportions and cutting style also play a crucial role.

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?

No, diamond carat and diamond size are not interchangeable. Carat is a precise metric unit that measures a diamond’s weight, not its dimensions. While it might seem intuitive to assume that a higher carat means a larger diamond, that’s not always the case. Relying solely on carat weight to estimate a diamond’s size can be misleading.


Different gemstones have varying densities, meaning two stones of the same carat weight may appear vastly different in size. Additionally, a diamond’s cut plays a significant role in how large it looks. A poorly cut round diamond, for instance, may carry excess weight in its depth or have an overly thick girdle. This ‘hidden’ weight doesn’t contribute to its visible size, so a 1.20-carat diamond with poor proportions may appear no larger than a well-cut 1-carat stone—despite the extra cost. Understanding these nuances ensures that buyers get the best balance of carat weight, visual appeal, and value.

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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