“What’s the diamond carat weight?”, or simply, “How big is your diamond?”
These are questions every recipient of a diamond engagement ring will inevitably be asked – usually more than once. After all, we’ve all been culturally conditioned to believe that “bigger is better” when it comes to gemstone size, and higher carat weight is associated with higher social status.
But here’s the thing: a diamond’s carat weight is not the same its size. Though there’s definitely a correlation between weight and size, the size of a 1 carat diamond, for example, can vary significantly depending on its shape and cut.
What’s more, bigger and heavier diamonds often often look worse than smaller and lighter ones!
This guide covers the ideal sizes for different diamond carat weights and shapes, why a diamond’s weight isn’t as important as jewelers and marketing campaigns may have you believe, and how to select the best diamond carat weight and size for you.
Diamond Carats and Sizes
What is a Diamond Carat?
A diamond carat is a unit of weight used to measure a diamond’s mass. One carat equals 0.007 ounces (0.2 grams) worth of diamond. Thus, a 1.5 carat diamond is 0.010 ounces (0.3 grams), a 2 carat diamond is 0.014 ounces (0.4 grams), and so on.
The word “carat” originates from the Greek word “keration,” which refers to a carob seed. These seeds were historically used as counterweights on balance scales to measure precious stones. Over time, “carat” became the standard unit for measuring gemstone weights.
Not to be confused with “karat”, though the two words have the same ancestor. A gold karat is a measure of gold purity.
Of the 4Cs of diamonds – cut, color, clarity, and carat weight – carat weight typically has the single largest impact on a diamond’s price.
What is Diamond Size?
Diamond size refers to the dimensions of a diamond when viewed face-up, as measured in millimeters.
The face-up size of symmetrical diamond shapes with a 1:1 ratio, such as the round brilliant or square-shaped princess cut, is determined by the diamond’s average girdle diameter.
For elongated and asymmetrical diamond shapes, such as the rectangular emerald cut or teardrop-shaped pear cut, the face-up size is estimated from its width x length measurements.
Size varies between different diamond shapes, with some appearing larger than others of the same carat weight. For instance, a well-cut 1 carat round brilliant diamond measures about 6.4mm across, while a 1 carat princess diamond is about 5.5mm in diameter.
TL;DR: A diamond carat is a unit of weight measurement equivalent to 0.007 ounces, while diamond size means how big a diamond looks when viewed face-up. Carat, shape, and cut all affect the appearance of size.
Diamond Carat to Size Charts
The charts below will help you understand the sizes of different diamond shapes in different carat weights.
One thing you’ll notice is that size doesn’t increase proportionally with the carat weight of a diamond. That is to say, a 2 carat diamond isn’t twice as big as a 1 carat diamond. For instance, a 2 carat round brilliant diamond measures 8.1mm across, which is only a 26.6% increase in face-up size from a 1 carat round diamond.
A couple of other things to keep in mind:
- The measurements provided are guidelines to help you visualize how your diamond will look. Not every diamond will have these exact measurements. Saying that, symmetrical 1:1 ratio shapes like the round brilliant should be within 0.1 millimeters of our measurements, provided they’ve been cut to a high quality standard.
- Most diamond shapes don’t have “fixed” outlines. The cushion cut, for example, can be either squarish or a rounded rectangle. We’ve provided measurements for the squarish cushion shape, but even in the more rectangular shapes, expect to find length x height variability between stones.
Round Brilliant Diamond
TL;DR: As shown in the charts above, diamond shapes have different face-up sizes. Shapes that appear largest for their carat weights are the marquise, oval, pear, emerald.
See also: The Top 12 Most Popular Diamond Shapes
The Importance of Diamond Cut
Diamond cut is a major factor that affects how the size of a diamond is perceived. A high quality cut maximizes a diamond’s brilliance, sparkle, and overall appearance, while a poor quality cut diminishes it.
Let’s say you’re comparing two diamonds of the same carat weight, but with vastly different cut qualities. The well-cut diamond is beautiful and captivating, and creates the impression of being larger than its carat weight. On the other hand, the poorly cut stone appears dull, discolored, and small for its carat weight.
In fact, even a well-cut .90 round diamond will look bigger and more beautiful than a 1 carat badly-cut diamond. Which goes to show that carat weight isn’t everything – you’re better off focusing on the diamond’s cut quality and beauty, rather than insisting on an arbitrary carat number.
Ideal, Shallow, and Deep Cut Diamonds
A diamond that’s cut to ideal proportions is crafted with mathematical precision, ensuring it interacts with light in the most dazzling way. This is the type of diamond you want. Ideally cut diamonds have both intense beauty and the advantage of appearing large for their carat weight.
Shallow cut diamonds are cut too shallow, allowing light to escape through the bottom of the stone. Yes, these diamonds appear larger when viewed from above, but they lack the intense sparkle and fire of ideally cut diamonds.
Deep cut diamonds have too much of their weight concentrated in the girdle and pavilion, giving them a smaller face-up appearance. Their excessive depth also lets light escape through the sides, which diminishes light performance.
Good to know:
A diamond cut to ideal proportions isn’t the same as an Excellent cut diamond. Excellent is the highest diamond cut grade awarded by the Gemological Institute of America (GIA), the most reputable independent diamond grading institution.
Somewhat confusingly, it’s also not the same as an Ideal cut diamond. Ideal was the highest cut grade given by the American Gem Society (AGS), which was the other premier provider of gemstone grading assessments before it closed its labs in 2022.
However, as we’ll explain in the next section, neither Excellent-graded or Ideal-graded diamonds are typically cut to ideal proportions. To make sure you get a diamond that is ideally cut, read our guide to diamond cut (linked below).
TL;DR: Diamond cut has a huge impact on both a diamond’s beauty and its perceived size. Always choose a diamond that’s cut to ideal proportions.
The Downsides of Large Diamonds
Large diamonds can look fantastic, provided they’re ideally cut and don’t have noticeable discoloration or flaws. These stones make a terrific statement, drawing eyes from across the room with that incomparable sparkle and beauty that only diamonds can provide.
Unfortunately, if you’re shopping for a diamond of 2 carats or more, you need to be extra vigilant that your stone measures up in terms of cut, color, and clarity. These key aspects of diamond quality tend to decrease as carat weight increases.
- Jewelers care more about diamond weight than cut quality. Just because a diamond cutter could cut a diamond to ideal proportions, they very likely won’t. Doing so would reduce the stone’s weight, and therefore its profitability. Non-ideal cuts are an issue with all diamonds, but especially larger ones. Diamond prices rise significantly the heavier a stone gets, which puts cutters under more pressure to preserve weight in heavier diamonds.
- Color and clarity characteristics are more noticeable in larger diamonds. A diamond of 2 carats or more tends to exhibit more color than a smaller stone, even within the same color grade. Likewise, a 2 carat+ diamond will often display inclusions more prominently than a lower weight stone of the same clarity grade.
If you want a larger carat weight stone that has beauty to match its size, then be prepared to pay a bit more in terms of color and clarity grades than you would for a smaller diamond, and – above all! – make sure your diamond is cut to ideal proportions.
TL;DR: Color and flaws tend to become more prominent as carats increase. Take care that any higher carat weight stone is ideally cut, eye-clean, and doesn’t show too much color.
Cost-Saving Tips for Diamond Carat Selection
Diamond Carats and Magic Sizes
Most consumers are strongly inclined to buy what are known as “magic sizes“: diamond weights at half, three-quarter, and full carat increments.
Diamond prices increase sharply at each of these weight increments. Meaning that with all other 4Cs being equal, a 0.5 carat stone costs noticeably more than a 0.45 carat one, a 0.75 carat stone costs noticeably more than a 0.70 carat one, and so on.
Magic size diamonds are popular due to the psychological gratification of being able to say that you have (for example) a 1 carat diamond. For many people, 0.95 carats just doesn’t feel the same – even though visually distinguishing between a 0.95 and a 1 carat stone is impossible.
Buying at just below the magic size price increments can help you to buy an indistinguishably smaller but more beautiful diamond, by redirecting what you would have spent on carat into a better quality cut.
Carat Weight vs. Total Carat Weight
When evaluating carat weight (abbreviated as “cw”), you’re focusing on the size of the center stone or primary diamond. For instance, a engagement ring may have a center diamond carat weight of 1 carat.
Total carat weight (abbreviated as “ctw” or “cttw”), on the other hand, refers to the combined weight of all diamonds in a piece of jewelry, such as a ring with multiple stones. So, if a 1 carat ring has additional side stones equaling 0.3 carats, then the total for the entire ring is 1.3 ctw.
Understanding the difference between the two is important because of how the weight of individual stones affects diamond pricing. To refer again to the example above, a single 1.3 carat diamond is worth more than three smaller diamonds with respective weights of 1 carat, 0.15 carats, and 0.15 carats (the weight of each of the two side stones).
In other words, you’d expect to pay less for a ring with 1.3 tcw than for a ring with 1.3 cw. Be wary of any unscrupulous vendors who try to say otherwise.
TL;DR: You can save significantly by buying your stone at just below “magic size” increments. Don’t be misled into overpaying for total carat weight, as most of a ring’s value is concentrated in its center diamond.
Recap: Diamond Carat Key Takeaways
In summary, our top points to keep in mind when deciding on your diamond carat weight are:
- Carat weight isn’t everything; a diamond’s shape and cut significantly affects its perceived size.
- A diamond’s size doesn’t increase proportionally with its weight.
- Flaws and color often do increase with carat weight.
- Try to avoid “magic sizes”; buying just below these increments offers better value.
- Don’t confuse carat weight with total carat weight.
Thanks for reading! If you’d like to learn more about diamonds, try out our guide to the twelve most popular diamond shapes.