What Does Carat Mean? Understanding Diamond Carat vs Size

Q: What does carat mean in diamonds?

Carat measures a diamond's weight, not its size. One carat equals 0.2 grams. Two diamonds of identical carat weight can look different in size depending on their cut and shape.

Q: Is a higher carat diamond always bigger?

No. A higher carat diamond is heavier, but not necessarily larger in appearance. Cut proportions and shape significantly affect how large a diamond looks.

Q: What is the best carat size for an engagement ring?

Most engagement rings feature diamonds between 0.5ct and 1.5ct. A well-cut diamond in any size will outperform a larger stone with a poor cut. The right size depends on your budget and partner's preferences.

Q: How many carats is a good engagement ring?

The average engagement ring diamond in Australia is approximately 0.8–1.0ct. Cut quality matters more than carat weight — a well-cut 0.7ct diamond will sparkle more than a poorly cut 1.2ct stone.

Diamond carat is one of the most misunderstood terms in jewellery. Most people assume it measures size, meaning how big the diamond looks. It doesn't. Carat measures weight, and the difference between those two things matters when you're trying to buy a diamond that looks right on the hand.

What is a carat?

One carat equals 0.2 grams, or 200 milligrams. The term comes from the carob seed, historically used as a counterweight in scales because of its consistent weight. The unit was standardised internationally in 1907.

Diamonds are also measured in points, where 100 points equals one carat. So a 0.75ct diamond is sometimes described as 75 points, and a 0.50ct as half a carat.

Carat vs size: the critical distinction

Two diamonds of identical carat weight can look noticeably different in size, depending on cut proportions and shape. A round brilliant with a very deep cut concentrates weight in the depth of the stone. It weighs as much as a shallower stone but looks smaller from above. A well-cut round brilliant with optimal proportions returns more of its weight to the face-up appearance.

Shape also affects face-up size significantly. An oval appears about 10 to 15% larger face-up than a round of the same carat weight, because its elongated silhouette covers more surface area. A pear, marquise or emerald cut can look larger still. That's one reason elongated shapes are so popular: more visible size per dollar spent.

How carat works with the other three Cs

Carat is only one of the four Cs. It's tempting to chase the biggest number, but a larger stone with a poor cut can look duller and smaller than a slightly lighter, well-cut one. Fix your budget, prioritise cut quality first, then choose the largest carat weight that still leaves room for a good cut. A 1.3ct stone that sparkles beats a lifeless 1.5ct every time.

Common carat sizes and what they look like

A 0.5ct round brilliant is approximately 5.1mm in diameter. A 1.0ct round is approximately 6.4mm. A 1.5ct round is approximately 7.3mm. Those give you a reference point, and once you know an oval of the same carat weight measures 7 to 8mm in length, the difference becomes tangible.

How many carats is the average engagement ring?

In Australia the average centre stone sits around 1.0 to 1.2 carats, though there's no right size. It comes down to the wearer's hand, style and budget. Because lab-grown diamonds cost considerably less than mined stones, many couples now choose 1.5ct or larger for the same spend.

Lab-grown diamonds and carat value

A lab-grown stone costs considerably less than a mined equivalent, so your budget stretches further in carat weight. The same spend that once bought well under a carat now comfortably buys more.

Browse our lab-grown diamond solitaire rings or learn more about diamond quality before you start shopping.