How to Read a Diamond Size Chart
A diamond size chart translates carat weight into a stone's actual millimetre dimensions — the measurement that decides how large a diamond truly looks on the hand. The distinction matters because a carat is a unit of weight (one carat equals 0.20 grams), not of size. Two diamonds can share the same carat weight yet look noticeably different face-up, depending on how they are cut. The chart above lists the approximate length and width for a well-cut diamond of each shape at every popular carat weight, so you can compare like with like before you buy.
Because a diamond's weight grows with the cube of its dimensions, size does not increase in a straight line with carat. Doubling the carat weight does not double the width — it increases each linear dimension by only about 26 percent. That is why a 2 carat round diamond measures roughly 8.2 mm across rather than double the 6.5 mm of a 1 carat stone. Our visualizer applies this cube-root relationship to every shape so the sizes you see stay true to life.
How Big Is a 1 Carat Diamond?
A well-cut 1 carat round diamond measures about 6.5 mm in diameter — a little wider than a garden pea and close to the size of a pencil eraser. In fancy shapes, one carat spreads differently: an oval is roughly 7.7 × 5.7 mm, an emerald cut about 7.0 × 5.0 mm, a princess cut around 5.5 mm square, and a marquise a slender 10 × 5 mm. Elongated shapes carry their weight along a longer outline, so they often appear larger on the finger than a round of the same weight, even when their actual surface area is similar. Switch shapes in the tool above and watch the true-to-scale hand update to see this for yourself.
Diamond Size by Shape
Every cut wears differently. Round brilliants deliver the most sparkle and a classic, balanced footprint. Oval and pear shapes elongate the finger and read large for their weight. Emerald and Asscher cuts are step-cut, trading fire for a clean, architectural look and an open table that can make a stone feel understated. Princess and radiant cuts pack brilliance into a modern square or cushion-corner outline. Cushion cuts soften the corners for a romantic, antique feel, while marquise and heart shapes make a distinctive statement. Because coverage differs, always compare the millimetre dimensions — not just the carat — when weighing one shape against another.
Why Two Diamonds of the Same Weight Can Look Different
Cut proportion is the hidden variable behind every size chart. A diamond cut too deep hides weight in its pavilion, so it looks smaller face-up than its carat suggests; a shallow stone spreads wider but can sacrifice brilliance. Table size, girdle thickness and overall make all shift the millimetre reading for a given weight. This is why the figures in any diamond size chart — including ours — are careful averages for well-cut stones, and why the exact measurements printed on a diamond's grading report are the numbers to trust before purchase.
Choosing the Right Diamond Size for Your Hand
The same diamond looks larger on a slender finger and more modest on a broader one, which is why our visualizer lets you place the stone on a range of ring sizes. As a guide, a smaller finger flatters delicate solitaires and elongated shapes, while a wider band and finger can balance a larger centre stone beautifully. Consider your setting, too: a halo of accent diamonds can make a centre stone appear a half-carat larger, and a slim band makes the same stone look bigger by comparison. When you have a size in mind, our ring size chart will help you find the perfect fit, and you can explore finished pieces in our engagement ring collection.
Diamond Size Chart FAQ
How many millimetres is a 1 carat diamond?
A well-cut 1 carat round diamond is about 6.5 mm in diameter. Fancy shapes vary: roughly 7.7 × 5.7 mm for an oval, 5.5 mm square for a princess, and 7.0 × 5.0 mm for an emerald cut.
Is a 2 carat diamond twice as big as a 1 carat?
No. It weighs twice as much, but because weight rises with the cube of the dimensions, a 2 carat round is only about 26 percent wider — roughly 8.2 mm versus 6.5 mm. Face-up, it looks larger but not double.
Does the shape affect how big a diamond looks?
Yes. Elongated shapes such as oval, marquise and pear cover a longer area of the finger and often look larger than a round of the same carat weight, even when the true surface area is comparable.
What is the most popular diamond size?
For engagement rings, centre stones between 1 and 1.5 carats are the most requested, offering a balance of presence and value. Use the slider above to see how each weight looks true-to-scale on a hand.
Are lab-grown and natural diamonds the same size per carat?
Yes. A lab-grown diamond and a natural diamond of equal carat weight and cut quality share the same millimetre dimensions, because they have the same physical and optical properties.
How do I measure a diamond's size?
Diamonds are measured in millimetres across their length, width and depth, listed on the grading report. Our visualizer estimates these from carat and shape, but always confirm exact dimensions from the certificate before you buy.