Last Updated October 2022 - 1 articles


Understand what a carat is and what it measures with expert advice and tips from our professionals.

Diamond Carat Size

by Willyou.net * Oct 3, 2021

Key Takeaways

  • Carat weight is one of the first things any shopper will think about when they start to plan their engagement ring.
  • Plenty of shoppers start off thinking that ‘carat’ correlates with size when, in fact, it’s a unit of measurement used in the world of gemology.
  • For that reason, two diamonds of the same shape and carat weight can appear to be different sizes, if one is proportioned better than the other. Deep or shallow cut diamonds will appear smaller or larger (respectively) than other diamonds of the exact same weight, cut to ideal proportions.
  • Carat weight is one of the most significant factors behind a diamond’s value.
0.70ct - 1ct - 1.5ct - 2ct - 3ct -Diamond Carat Size

When it comes to diamonds, bigger doesn’t always necessarily mean better. Even engagement rings – the ultimate landing place for any diamond – can stand out as true winners without needing to rely on a 10 carat stone to make them impressive.

But we’re getting ahead of ourselves. First of all, it pays to understand exactly what we (and your jeweler) mean by the term ‘carat’ before you start worrying over your own diamond’s carat

What is the Carat of a Diamond?

Carat is a specific weight measurement used on gemstones and pearls. It is equal to 0.2 grams, or 200 milligrams.

This unit of measurement is used around the world, meaning that, while it doesn’t tell us anything concrete about a diamond’s surface diameter, it’s pretty easy to gauge a rough idea based off carat alone (more on that below).

Carats are also assigned points

What are Diamond Carat Sizes?

While the most common tiers are 0.5, 1, 1.5, 2, and, after that, whole carat increments, a diamond’s carat weight can be any number, though it is carried out to two decimal places.

As you might have noticed by now, diamonds that weigh less than one carat can be presented as fractions or decimals of 1 carat. A 0.5 carat diamond, for instance, weights exactly 100 milligrams, while a 0.1 carat diamond will weigh 20 milligrams, or 0.02 grams – or, alternatively, 1/10th of a carat.

Since carat is shown to two decimal places, weight may be rounded up – although not in the case of magic sizes, which we will look at just below.

For now, however, we’ll leave you with this. A diamond that weighs 234.9 milligrams will be presented as 2.35 carats, while a diamond that weights 199.7 will be presented as 1.99 carats, rather than 2. You might already be able to work out why that is but, if not, here’s a brief explainer on ‘magic diamond sizes’.

What are Magic Sizes?

A magic size, like 0.5, -.75 or 1 carat, are considered to be more sought-after than diamonds that sit between these sizes.

If you’re hoping to use a 1 carat diamond in your engagement ring, then the odds are that you’re less likely to settle instead on a 0.99 carat diamond. It’s not unheard of, and can be a good way of saving a little money but, in general, the emphasis is placed on quarter- and half-sizes (whether that’s 0.25 carats, 1 carat, 1.5 carats), rather than the many sizes that exist in-between.

This is why the 199.7 carat diamond would not be rounded-up to 2 carats, while the 234.9 carat diamond could be presented as a 235 carat stone.

There is, of course, no noticeable difference between a 0.49 carat diamond and a 0.5 carat diamond, or a 0.99 carat diamond and a 1 carat diamond, but, for obvious reasons, they are the more popular sizes among buyers.

What do Points Mean on Diamonds?

Points are typically used for smaller diamonds below 1 carat in weight. 100 points is equal to 1 carat, meaning that 1 point is equal to a 0.01 carat diamond.

This is another useful way of conveying the weight of any given diamond, as it allows a more precise means of conveying a diamond’s weight – particularly when that diamond is very small.

Melee diamonds, or the very low carat weight diamonds typically used in halo and pavé settings, generally fall below 1/10th of a carat. In these instances, it can be easier for 0.07 carat diamonds be to refer to as 7 pointers, for instance.

How Much is a 1 Carat Diamond Worth?

A 1 carat diamond can be as little as $,2000 (in some cases, even less), but a 1 carat diamond of a good quality will cost considerably more – anywhere up to around $12,000.

Diamonds are not priced according to their carat weight alone, although it is a pretty major factor behind that final price tag. The rest of the Four Cs – cut, clarity and color – all influence a diamond’s value significantly. This is why two 1 carat diamonds can differ in value by thousands of dollars.

Those five-figure values are typically reserved for diamonds with exceedingly good grades – particularly with regard to clarity and color. An Internally Flawless (IF) diamond with a D or E color grade, for instance, will be much more expensive than an eye clean VS2 diamond with an H or I color grade, despite the fact that they will look very similar.

Shape is also a major factor behind value. Round diamonds are the most popular, and among the most difficult to perfect. They also result in quite a lot of wastage, meaning that they are far more expensive than the less popular shapes, such as the Emerald cut.

2 carat oval diamond engagement ring -Diamond Carat Size

How Big is a 1 Carat Diamond?

Carat is a term that refers to weight only – not size. However, a 1 carat round diamond (cut to ideal proportions) will generally measure around 6.4mm in diameter, while a square shape like the Cushion cut will measure around 5.76mm.

The most important thing to keep in mind when it comes to size is the fact that different shapes lead to different surface areas, even when all diamonds are the same carat weight. The ideal cut proportions for some diamonds are deeper than others, meaning that the same amount of weight is ‘carried’ differently across the shapes.

In general, rounder shapes appear larger than square or rectangular diamonds. Oval and Marquise cuts tend to look a little larger than Round cuts, while the Cushion, Emerald and Asscher appear smaller.

How Many Carats is the Average Engagement Ring?

In the US, the average carat weight for the center diamond in an engagement ring is around 1 – 1.2 carats, although current trends seem to be leaning in favor of diamonds above this popular grade.

We mentioned above that a 1 carat Round diamond (cut to ideal proportions) will feature a diameter of around 6.4mm. And, while each shape will vary a little in terms of surface area, this is a great size to place at the center of any ring. It’s big enough to draw the eye even in a diamond solitaire, or to stand out in a more elaborate setting such as a halo or a split shank.

One carat diamonds also offer plenty of room for shoppers of all budgets. Opting for a lower clarity grade (while still staying eye clean) and a Near Colorless grade (as opposed to Colorless) makes it possible for shoppers on tighter budgets to create stunning rings that don’t snowball out of a suitable price point.

Bigger diamonds command higher prices. A visibly included 3 carat diamond, for instance, will still be significantly more expensive than an eye clean 1 carat diamond – another reason why 1 carat is a great starting point for many shoppers. It checks plenty of boxes.

Is a 0.5 Carat Diamond Too Small?

0.5 carats is generally considered pretty small for the center stone of an engagement ring, but there’s no such thing as ‘too small’ – it all comes down to personal preference.

In the US, the average engagement ring features a diamond that falls around 1 carat. This means that, in all likelihood, the bulk of engagement rings you’ve encountered before were probably over 0.5 carats in weight, so a diamond of this size might look a little more modest than what you’re used to.

That said, a beautiful, eye clean half-carat diamond can look truly stunning in the right setting, and there are ways of complementing a smaller surface area with the ring. For instance, using a halo can create the illusion of extra weight, as well as using a warmer-toned metal to contrast with the stone, and help it to stand out more.

More important than the size of your diamond are cut quality and eye cleanliness – everything else comes second.

Is Carat the Same as CTTW?

No. Carat is often abbreviated to CT., but CTTW refers to something else entirely.

CTTW stands for Carat (CT) Total Weight (TW), and is used as a way of conveying the collective carat weight of multiple diamonds, particularly when they are already cast within jewelry. You can read our in-depth explainer on CTTW but, for now, it can be helpful to see it this way:

A piece of jewelry featuring many diamonds, such as this Cushion Cut Halo Engagement Ring, will feature a CTTW – a sum of the individual carat weights of each diamond, including the center stone. A piece of jewelry featuring just one diamond, like this Cushion Cut Cathedral Engagement Ring, won’t need a CTTW – just a carat weight for the single diamond.

What is the Difference Between Carat and Karat?

A diamond’s carat is its weight, while the proportion of gold to its alloys is measured in karats.

This is something that can easily trip-up first-time buyers of fine jewelry as, unless you’re looking exclusively at platinum for your ring, both diamond carat and gold karat are bound to crop up pretty frequently.

The most important thing to understand is that, while the two terms sound similar, they refer to totally different things.

Rather than weight or size, karat represents 1/24th of a piece of gold, meaning that 24 karat gold is totally pure. Unfortunately, pure gold is way too soft and damage-prone to be used in jewelry, so it’s alloyed with other, strengthening metals – which, in turn, drive down the purity of that piece of gold. 18 karat gold, then, is 18 ‘parts’ gold to 6 ‘parts’ alloying metals, like silver, palladium, or platinum.

Interestingly, this is why rose gold (which takes its pink-ish color from copper and silver) could never be 24k, and why it’s so much stronger than 24k gold.

So the term ‘karat’ (confusingly spelled carat outside of the US) refers to proportion, while carat is exclusively used as a unit of measurement for gemstones.


How to Tell the Carat Size of a Diamond

The easiest way to find out the carat size of any diamond is to check its GIA Report. This will have been completed by two expert diamond graders, who will have used incredibly precise scales to ascertain the exact weight of the diamonds they grade.

Furthermore, your jeweler will be able to offer you all the insight you could need into this aspect of your diamond, and more besides.

So, Which Diamond Carat is Best?

There is no ‘idea’ carat weight for any piece of jewelry – particularly engagement rings. The best thing you can do is learn about this unit of measurement, and how to make it work for you.

It’s not always easy wrapping your head around the specifics of diamond carats. For one thing, it’s pretty difficult to gauge a rough price point for any specific carat weight, given the massive discrepancies that can exist between one diamond and the next – even if they are exactly the same carat weight. 

For another, the different ways individual jewelers and experts present a diamond’s carat weight can mean you have to do some mental gymnastics to get it all straight in your head. In other words, when a seventy-three pointer means the same thing as a 0.73 carat diamond – which might also be presented as 0.73 ct or ¾ of a carat – it’s not always easy to keep your head straight.

Still, it won’t take long before you start to feel more comfortable with this particular unit of measurement – and, in particular, with using it as a way of sorting through the massive numbers of diamonds on the market today to find one that is perfect for your vision for that ring.

So, in essence, look at it this way: you’re learning about carats in order to make a good decision further down the line. You’re not, however, learning about carats in order to find out what carat weight is ‘right’. That’s something you can only know when you’ve taken cut, clarity, color, cost and your future bride’s tastes into account.