The Diamond 4Cs: Cut, Colour, Clarity & Carat

The 4Cs system -- Cut, Colour, Clarity, and Carat Weight -- was developed by the Gemological Institute of America (GIA) in the 1950s and has since become the universal standard for evaluating diamond quality. Before this framework, there was no consistent way to describe or compare diamonds, making the buying process opaque and confusing for consumers. Today, the 4Cs provide a common language that allows you to objectively assess any diamond, whether mined or lab-grown, anywhere in the world.

Each of the 4Cs contributes to a diamond’s overall beauty, rarity, and price. However, they do not all have equal visual impact. Cut has by far the greatest influence on how beautiful a diamond looks to the eye, while colour and clarity affect beauty only at extreme ends of their respective scales. Carat weight, meanwhile, primarily determines the diamond’s size and has the most straightforward relationship to price.

Understanding the 4Cs is not about memorising grades -- it is about knowing which factors matter most for your particular purchase and where you can make strategic compromises to maximise beauty within your budget. The following sections will give you the detailed knowledge to do exactly that, whether you are shopping for an engagement ring or any other diamond jewellery.

Cut is the single most important factor in determining a diamond’s visual beauty. It refers not to the shape of the diamond (round, oval, etc.) but to the quality of its proportions, symmetry, and polish -- how well the diamond’s facets interact with light. A masterfully cut diamond captures light entering through the top, bounces it between its internal facets, and returns it through the crown in a display of brilliance (white light), fire (spectral colours), and scintillation (sparkle as the diamond moves).

When a diamond is cut too shallow, light escapes through the bottom before it can be reflected back. When cut too deep, light leaks out the sides. In both cases, the diamond appears dull and lifeless compared to an ideally proportioned stone. This is why cut grade matters more than any other quality factor: a mediocre diamond with a perfect cut will look more beautiful than a high-colour, high-clarity diamond with a poor cut.

Cut Grade Scale

For round brilliant diamonds, the cut grade is included on every IGI and GIA certificate. Fancy shapes (oval, cushion, emerald, etc.) do not receive a formal cut grade on most certificates, but you can evaluate their cut by looking at proportions, symmetry, and polish grades. The key measurements to examine for round brilliants are table percentage (54-57% ideal), depth percentage (61-62.5% ideal), and crown angle (34-35 degrees ideal).

Our recommendation is straightforward: always choose Excellent or Ideal cut for round brilliants, and look for Excellent symmetry and polish for all shapes. This is the one area where we advise never compromising, regardless of budget. The difference in beauty between an Excellent and Good cut is far more visible than the difference between a D and G colour or a VVS1 and VS2 clarity.

Diamond colour grading measures the absence of colour in a white diamond. The scale runs from D (completely colourless) to Z (light yellow or brown), with each letter representing a narrow range on the colour spectrum. Colourless diamonds are rarer and therefore more expensive, but the differences between adjacent grades are extremely subtle and often imperceptible without side-by-side comparison in controlled laboratory conditions.

The colour grading process is performed by trained gemologists who view the diamond upside down against a neutral white background, comparing it to master stones of known colour grades. This is done because viewing a diamond face-up (as you would wear it) makes colour differences nearly impossible to detect -- the brilliance and fire of a well-cut diamond effectively masks body colour.

Colour Grade Scale

Our recommendation for most buyers is the G-H colour range. These near-colourless diamonds appear white when set in any metal and cost 20-30% less than the D-F colourless range. The savings can be substantial -- often enough to upgrade the diamond by a full carat size or improve the cut grade. If you are choosing a yellow or rose gold setting, I-J colour represents outstanding value.

Clarity measures the presence, size, number, position, and nature of inclusions (internal characteristics) and blemishes (surface characteristics) in a diamond. These features are the natural fingerprints that form during a diamond’s creation, whether in the Earth’s mantle or in a laboratory. Most are microscopic and have no impact on the diamond’s beauty or structural integrity when viewed at normal distances.

Clarity is graded under 10x magnification by trained gemologists. This is critical to understand: the grading standard is not based on what you can see with the naked eye but on what is visible under laboratory-grade magnification. This means that many clarity grades that sound significantly different (VVS2 vs. VS1, for example) produce diamonds that look absolutely identical to the unaided eye.

Clarity Grade Scale

Clarity and Diamond Shape

The importance of clarity varies by diamond shape because different faceting patterns hide inclusions differently. Brilliant-cut shapes like round, oval, cushion, and radiant have many small facets that break up light into a complex sparkle pattern, making inclusions harder to see. These shapes are forgiving and SI1 clarity is often perfectly eye-clean.

Step-cut shapes like emerald and Asscher have large, open facets that act like windows into the diamond. Inclusions are much more visible in these shapes, so we recommend VS2 or higher clarity for step-cut diamonds. The clean, hall-of-mirrors effect that makes these shapes so beautiful demands a clear interior.

Our recommendation for most buyers: VS2 clarity. It is almost universally eye-clean across all shapes, provides excellent value, and the savings over VVS and Flawless grades are substantial -- typically 15-25% -- with zero visible difference when worn.

Carat is the standard unit of weight for diamonds and gemstones. One carat equals exactly 0.2 grams, or 200 milligrams. The term originates from carob seeds, which were historically used as counterweights on balance scales because of their remarkably uniform weight. Today, carat weight is measured with extreme precision to the hundredth of a carat using digital scales.

It is essential to understand that carat measures weight, not physical size. Two diamonds of the same carat weight can look noticeably different in size depending on their shape, cut proportions, and depth. A deeply cut diamond may carry more of its weight in the pavilion (bottom), resulting in a smaller face-up appearance. A well-proportioned diamond distributes its weight to maximise the surface area visible from above.

Carat Weight and Approximate Dimensions

The “Magic Sizes” Price Effect

Diamond prices do not increase linearly with carat weight. Instead, they jump at certain psychologically significant thresholds known as “magic sizes”: 0.50ct, 0.75ct, 1.00ct, 1.50ct, and 2.00ct. At each threshold, per-carat pricing increases sharply due to market demand and perceived value. A 1.00-carat diamond might cost 15-20% more per carat than a 0.95-carat diamond of identical quality, despite the two being visually indistinguishable.

This creates a powerful value strategy: buying just below these thresholds. A 0.90-carat diamond looks virtually the same as a 1.00-carat to the naked eye (the diameter difference is roughly 0.3mm -- less than the thickness of two sheets of paper), but can cost significantly less. This savings can be redirected to higher cut quality, a better setting, or simply kept in your pocket.

Shape and Perceived Size

Elongated shapes offer a distinct advantage in perceived size. An oval diamond has approximately 10% more surface area than a round brilliant of the same carat weight, making it appear substantially larger. Marquise and pear shapes offer even greater perceived size advantages. If maximising how large your diamond looks is a priority, these shapes deliver outstanding value.

The art of buying a diamond is not about maximising each C individually -- it is about finding the optimal balance that produces the most beautiful diamond within your budget. A $5,000 diamond with perfect balance across the 4Cs will outperform a $7,000 diamond where the budget was poorly allocated (for example, overspending on colour while under-investing in cut).

Let us illustrate with a practical example. Suppose you have a budget of $6,000 for a lab-grown diamond. You could buy a 1.0-carat, D-colour, VVS1, Very Good cut diamond -- impressive on paper but underperforming in person due to the cut grade. Alternatively, you could buy a 1.3-carat, G-colour, VS2, Excellent cut diamond. The second option is 30% larger, equally beautiful to the naked eye, more brilliant and sparkly, and costs the same. The difference is entirely in how you prioritise the 4Cs.

Every diamond purchase is unique, and the “ideal” balance depends on personal preferences and priorities. Some buyers value size above all else; others want the purest colour regardless of carat weight. Our team at Aurela Diamonds specialises in helping you find the perfect balance. We will walk you through options side by side until you find the diamond that feels right. To get started, explore our Engagement Ring Buying Guide or Diamond Buying Guide for more context on the complete purchase process.