Carat is among the most common terms when shopping for diamonds and engagement rings. In this article, we’ll teach you everything you need to know to understand how diamond carat sizes work.
What Is A Carat?
A carat is a unit of measurement used to determine the weight of a diamond. Carats are actually an ancient unit of mass rather than weight. Seeds of the carob tree have always been used to weigh gold and diamonds since the early 16th century. Diamond traders used carat weight because they believed—wrongly, as it turned out—that all seeds were identical in size and weight.
In 1907, the carat weight was standardized at 200mg. It has since become the official metric used when buying diamonds. When weighed on a metric scale, a 1.00-carat diamond weighs 200mg, and a 2-carat diamond weighs 400mg.
Pro Tip: Carat indicates a diamond’s weight, not its size or dimensions.
Does Carat Size Matter?
Simply put, yes. Carat weight is one of the most significant factors that determines a diamond’s price. While color, clarity, and cut help determine the grade of the diamond, carat size significantly impacts its value, usually more than any other characteristic.
As the size of a diamond increases, so does the price. Furthermore, because larger, high-quality diamonds are rarer than smaller sizes, we have the effect of “the total is more valuable than the sum of its parts” coming into play. Therefore, a larger diamond will cost significantly more than two smaller diamonds with the same combined weight.
Diamond Size and Carat Weight
Diamond size is one of those things that causes some confusion. This is because the term “carat size” isn’t an accurate definition. When we talk about the “size” of a diamond, we’re really discussing the weight as measured in carats.
This is important to understand because how big a diamond appears to the eye is less connected to the carat size than you might assume. When most people notice how large a diamond looks, what they’re really noticing is how large the surface area of the top of the diamond is.
The Anatomy of a Diamond
Looking at the diagram below, we can see that a diamond’s surface area or “table/crown” is the area we see when looking at a set diamond. The lower part of the diamond (the pavilion) doesn’t actually contribute to how large the diamond appears when in a setting, even though it does contribute to the diamond’s weight and, subsequently, the cost.
You might ask, why not cut a diamond differently? If the table/crown size determines how large a diamond appears, why not make the pavilion more shallow and increase the table size so we can maximize the visible size of the diamond for its weight?
The reason for this is that the quality of the diamond’s cut affects its brilliance. If a diamond is cut too shallowly or, for that matter, too deeply, it won’t reflect light effectively, making it appear less brilliant. Therefore, when evaluating a diamond, how proportionally its cut affects its grade and overall value.
Look at the diagram below to understand how a diamond is cut and how it affects its ability to reflect light.
As you can see, both a diamond that’s cut too shallowly and one that’s cut too deeply will poorly reflect light. A proportionately cut diamond, however, will refract light beautifully, giving the diamond a sparkling appearance.
This is why, even though it may be tempting to cut a diamond with a very shallow pavilion (bottom half) in order to maximize the table size, no reputable jeweler will actually do so, as it negatively impacts the diamond’s brilliance and devalues the diamond.
How a Diamond’s Cut Affects its Diameter
Considering what we established above, we understand that you can have two diamonds of the same shape and carat weight but with different surface sizes.
For example, you can have two round brilliant cut diamonds that both weigh 1 carat but have different surface diameters. The more deeply cut diamond will have a smaller diameter because more of the volume is taken up by the pavilion or other parts of the diamond. The more shallowly cut diamond will have a larger diameter because the pavilion takes up less space.
The diamonds shown in the image above are equal in all measures except cut quality. They both weigh exactly 1 carat and carry H-color and VS2 clarity grades. Despite having equal weights, when viewed from the side profile, you can see a marked difference in the dimensions of each diamond. Diamond A, graded as ‘Excellent Cut,’ has a proportional ratio of diamond table to the pavilion and a surface diameter of 6.51mm.
Conversely, Diamond B carries a lower quality cut grade, and we can see that the crown height is larger, resulting in a less proportional-looking diamond and a smaller surface diameter of 6.21mm.
This difference in cut quality is also apparent when viewing the diamond from the top. The more deeply cut diamond appears to have lots of dark areas in the center, which diminishes the brilliance and sparkle of the the stone.
The Correlation between Carat Weight and Visible Size
As mentioned above, when we say “carat size”, we really mean ”weight,” as opposed to visible size. Visible size is a major factor in a diamond’s appeal, though the progression in size isn’t as pronounced as you might expect.
When you buy most commodities by weight, two units usually give you twice as much as 1 unit. Although the same is true of diamonds, as mentioned above, there is something akin to an iceberg principle at play. This means a diamond’s weight and diameter don’t increase at equal rates.
Size Difference Between a 1-carat and 2-carat
For example, with modern round brilliant cut diamonds (although this similar principle applies to all cuts), a 1-carat diamond will be 6.5mm across the widest point, and a 2-carat diamond will be 8.2mm across, not 13mm as might be expected. See the example below.
In other words, even though the 2-carat diamond is twice as heavy, it doesn’t appear twice as big. When setting a 2-carat diamond in a ring, it won’t appear much larger than the 1-carat diamond. You will only see the surface area increase by approximately 25-26% over that of a 1-carat diamond.
Pro Tip: Though a larger diamond won’t appear as big as you might assume, you’re not getting less diamond; you’re just seeing less of what you pay for.
Diamond Dimensions by Carat Weight
Now that we understand the correlation between carat weight and visible size let’s look at the diamond sizes of each carat weight. Note that all dimensions are approximate. Additionally, as mentioned above, these dimensions can vary depending on the type of cut and the corresponding crown area size.
| Carat Weight | Round Brilliant | Emerald Cut | Asscher Cut | Cushion Cut | Oval Cut | Pear Cut | Marquise Cut | Princess Cut |
|---|---|---|---|---|---|---|---|---|
| 0.5 ct | 5.2 x 5.2 mm | 5.0 x 3.5 mm | 5.0 x 5.0 mm | 4.5 x 4.5 mm | 6.0 x 4.5 mm | 6.0 x 4.0 mm | 8.0 x 4.0 mm | 4.5 x 4.5 mm |
| 1.0 ct | 6.5 x 6.5 mm | 7.0 x 5.0 mm | 6.5 x 6.5 mm | 5.5 x 5.5 mm | 8.0 x 6.0 mm | 8.0 x 5.0 mm | 10.0 x 5.0 mm | 5.5 x 5.5 mm |
| 1.5 ct | 7.5 x 7.5 mm | 8.0 x 5.5 mm | 7.5 x 7.5 mm | 6.0 x 6.0 mm | 9.0 x 7.0 mm | 9.0 x 6.0 mm | 11.0 x 5.5 mm | 6.0 x 6.0 mm |
| 2.0 ct | 8.2 x 8.2 mm | 8.5 x 6.0 mm | 8.2 x 8.2 mm | 6.5 x 6.5 mm | 10.0 x 8.0 mm | 10.0 x 6.5 mm | 12.0 x 6.0 mm | 6.5 x 6.5 mm |
| 2.5 ct | 8.9 x 8.9 mm | 9.0 x 6.5 mm | 8.9 x 8.9 mm | 7.0 x 7.0 mm | 11.0 x 9.0 mm | 11.0 x 7.0 mm | 13.0 x 6.5 mm | 7.0 x 7.0 mm |
| 3.0 ct | 9.4 x 9.4 mm | 9.5 x 6.5 mm | 9.4 x 9.4 mm | 7.5 x 7.5 mm | 11.5 x 9.5 mm | 11.5 x 7.5 mm | 14.0 x 7.0 mm | 7.5 x 7.5 mm |
| 3.5 ct | 9.9 x 9.9 mm | 10.0 x 7.0 mm | 9.9 x 9.9 mm | 7.8 x 7.8 mm | 12.0 x 10.0 mm | 12.0 x 7.5 mm | 15.0 x 7.5 mm | 8.0 x 8.0 mm |
| 4.0 ct | 10.4 x 10.4 mm | 10.5 x 7.5 mm | 10.4 x 10.4 mm | 8.0 x 8.0 mm | 12.5 x 10.5 mm | 12.5 x 8.0 mm | 15.5 x 8.0 mm | 8.5 x 8.5 mm |
| 4.5 ct | 10.8 x 10.8 mm | 11.0 x 8.0 mm | 10.8 x 10.8 mm | 8.4 x 8.4 mm | 13.0 x 11.0 mm | 13.0 x 8.5 mm | 16.0 x 8.5 mm | 9.0 x 9.0 mm |
| 5.0 ct | 11.2 x 11.2 mm | 11.5 x 8.5 mm | 11.2 x 11.2 mm | 8.8 x 8.8 mm | 13.5 x 11.5 mm | 13.5 x 9.0 mm | 16.5 x 9.0 mm | 9.5 x 9.5 mm |
| 5.5 ct | 11.6 x 11.6 mm | 12.0 x 9.0 mm | 11.6 x 11.6 mm | 9.2 x 9.2 mm | 14.0 x 12.0 mm | 14.0 x 9.5 mm | 17.0 x 9.5 mm | 10.0 x 10.0 mm |
| 6.0 ct | 12.0 x 12.0 mm | 12.5 x 9.5 mm | 12.0 x 12.0 mm | 9.5 x 9.5 mm | 14.5 x 12.5 mm | 14.5 x 10.0 mm | 17.5 x 10.0 mm | 10.5 x 10.5 mm |
Look at the graph below to get a visual idea of how large a round brilliant diamond will appear for its carat weight. The bottom of the graph depicts the approximate size to scale, while the top section demonstrates the size comparison when magnified by 2x.
Diamond Dimensions by Shape
Another major factor in how large a diamond will appear for its weight is the shape of the diamond. Some diamond shapes have larger surface areas (crowns) than others. As a result, certain diamond shapes will appear larger than other shapes of the same carat weight.
The graph below shows the approximate dimensions for each diamond shape based on its carat weight. As you can see, marquise, pear, and oval cuts give a larger appearance than Asscher or cushion cuts.
So, if your goal is to maximize the visible size of your diamond once set, choosing a particular shape can help you get a larger looking stone.
How Carat Size Affects a Diamond’s Price
With diamond pricing, it’s important to remember that the total is worth more than the sum of its parts. Therefore, one large diamond is worth far more than two smaller diamonds, even though their combined weight is the same.
Below is a graph demonstrating how the price of a J-color and VS2-clarity round brilliant diamond increases with carat size. Note that the amounts listed reflect market prices as of June 2024.
| Carat Weight | price |
|---|---|
| 0.5 ct | $900 |
| 1.0 ct | $4,300 |
| 1.5 ct | $9,600 |
| 2.0 ct | $17,600 |
| 2.5 ct | $22,000 |
| 3.0 ct | $40,500 |
| 3.5 ct | $47,250 |
| 4.0 ct | $70,000 |
| 4.5 ct | $78,750 |
| 5.0 ct | $107,500 |
As diamonds get bigger, they become progressively rarer, which dramatically increases the price. Therefore, a diamond that measures twice the size of another of the same specs will cost many times the price rather than just twice the price.
How Big the Diamond Will Look on the Finger
The size of a diamond as it appears on a hand will depend on more than just its carat size. Several other factors impact the perceived size of a diamond when it’s worn in a ring.
Firstly, the size of the finger will affect how large the diamond appears. A diamond will appear smaller in relation to a wider finger than it would on a thinner finger.
Secondly, the diamond’s shape and cut determine its surface size, impacting how large it looks on the finger.
Another major contributor to how large a diamond looks is its setting. The height of the setting, the size, shape, and placement of the accent stones, and the width of the band. These all play a role in determining how large a diamond will appear to the eye.
The images below depict how diamonds of different carat weights appear on an average woman’s hand size. Note that the image and diamond dimensions may not be perfectly to scale.
To see more examples of different diamond sizes on a finger, click here.
Getting the Best Deal for Carat Size
Sellers always bundle the prices for diamonds within 0.50 carat intervals.
What this means is that a 0.95ct diamond will usually cost almost the same as one at 0.51ct and yet be visibly indistinguishable in size from a 1.00ct diamond. Once you know this you can take advantage of this information to get a better deal for your money.
Of course, this technique works the same in reverse as well. If you do eventually come to sell the ring, don’t expect more than the 0.50ct price for your 0.95ct diamond.
Buying Tips to Get a Larger-Looking Diamond
Assuming you’re working with a budget, here are tips to ensure you get the largest diamond for your price point.
1. Pay Attention to Carat Intervals
As mentioned, diamonds are priced at half-carat intervals. By selecting carefully, you can get a stone that’s nearly half a carat larger for the same price. Look for a diamond at the top of 0.50-carat intervals, like 0.98 or 2.49 carats. See our comments above.
2. Compromise on the Other Qualities
Find a larger diamond and sacrifice the clarity, cut quality, or color. Most buyers would rather have a few slight inclusions or a slightly yellower stone than a smaller diamond. This can be particularly helpful because diamonds of certain color and clarity grades offer similar appearances to the naked eye of those of higher grades but at a significantly lower price. Read our complete guides to diamond color and clarity to understand which grades offer the best value for money.
3. Utilize a Halo Mounting
Ask the jeweler to build a mounting with a halo around the center diamond. The halo will make the center diamond appear larger. And since the stones used in a halo are far better value (remember, smaller stones of the same total weight = less costly), you can get the effect of a much larger diamond without the price tag of a diamond of a larger carat weight.
Have a look at the ring above. The halo expands the appearance of the diamond’s total surface area, giving the effect of a much larger diamond. However, not every type of halo will be as successful at enlarging the appearance of the diamond. Make sure your jeweler knows what effect you’re aiming for. A seasoned jeweler can help you select a setting that best enhances the diamond’s size.
4. Choose a High Set Mounting
The height of a ring’s mounting refers to how close or far to the band the center diamond is set. A high-set ring features a diamond that sits further from the finger. This makes it appear more prominent and gives it the allusion of a larger size.
The three rings featured below demonstrate how the ring’s setting can increase or decrease the prominence of the diamond.
Ring A utilizes a bezel setting, with the diamond set very close to the band, giving the diamond a flatter and less prominent appearance.
Rings B and C are both set in prongs. However, Ring C is set significantly higher off the band than Ring B, which causes it to protrude further from the finger, making it more noticeable.
We hope you found our guide on diamond carat size helpful. If you’re considering purchasing a diamond ring and ready to take the next step, reach out to one of our expert jewelers here at Estate Diamond Jewelry. We’re here to help you select the best diamond and mounting for your preferences and budget.
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