If you’re shopping for an engagement ring, you need to know about carat weight — the unit used to measure the weight of a diamond. Carat weight is important because it determines the price of a diamond and reflects its rarity. We’ll explain it to you in detail.
1. What is carat weight?
Carat weight (ct) is one of the 4Cs of diamond quality . The 4Cs are a universal standard created by GIA to describe the attributes that determine a diamond’s value. The other “Cs” refer to color , clarity , and cut . Diamonds are weighed in carats, an international unit of measurement for gemstone weight. One carat is equal to 1/5 of a gram (0.20 grams).
The seeds in carob pods are so uniform in size (averaging about 0.197 grams) that early gem traders used them as weights in their scales. The word “carat” comes from the Greek word for carob, keratien, which also means very light.
The metric carat is divided into 100 points, abbreviated as pt. An easy way to remember this is to think of carats as dollars and points as cents. They are even written the same way: $1.54 means 1 dollar and 54 cents, while 1.54ct means 1 carat and 54 points. Don’t confuse the “carat” of diamonds with the “karat” of gold. Karat is a unit of measurement for the fineness of gold , abbreviated as “K” or “Kt” (note that in the UK, “carat” is used to describe both the weight of gemstones and the fineness of gold).
2. How is carat weight measured?
Diamonds are typically weighed using an electronic microbalance. The GIA laboratory weighs diamonds to five decimal places (1.12345), or one hundred-thousandth of a carat, to ensure the highest degree of accuracy. However, the industry often reports diamond carat weights to two decimal places (1.12), or one hundredth of a carat. GIA uses a stricter rule than normal mathematical rounding, rounding weights only to the 9th place. For example, a diamond weighing 1.128 carats would be rounded down to 1.12, while a diamond weighing 1.129 carats would be rounded up to 1.13. The rounded-off percent weight is then included on the diamond’s grading report. IMPORTANT: Because the price of a diamond is calculated by multiplying its carat weight by the price per carat, you should make sure the diamond you are purchasing is weighed accurately. You should also make sure the diamond’s weight is accurate to two decimal places. Why? A 0.97 carat diamond is not the same as a one carat (1.00 carat) diamond. If two diamonds have the same color, clarity and cut quality, their price should reflect the difference in size.
Large diamonds are rarer than small ones, which is one reason this 5.07 ct. gem is so stunning.
3. Carat weight and diamond size are not the same thing.
It may sound like common sense that equal carat weights are equal in size, but this isn’t always the case. Different gem materials have different densities (mass per unit of volume), so two gems of exactly the same carat weight may actually be very different sizes. For example, rubies are denser than diamonds, so a one-carat ruby will appear smaller than a one-carat diamond. Also, the way a gem is cut can affect perceived size, and a poorly cut round brilliant diamond may be too deep or have a thick girdle. There may be extra weight hidden in the middle or below the girdle. Once the diamond is set, you won’t see the “hidden” carat weight, so a poorly cut 1.20 carat diamond may appear the same size as a well-cut 1.00 carat diamond. You end up paying for the extra weight without getting the benefit of it. In this case, the diamond’s cut grade, not just the carat weight, is even more important. Bottom line: You shouldn’t judge a diamond’s size based on its carat weight alone. If it is a round brilliant cut diamond, you should check the diamond cut grade (available on your GIA diamond grading report) to ensure that the diamond is well cut and you are not paying for meaningless weight. Learn more about cut: GIA Diamond Cut Grade: Six Things to Consider
The diamond on the right has a much thicker girdle, which makes it heavier. A thicker girdle does not provide any visual advantage, but the added weight makes the diamond more expensive than the one on the left. When mounted in a ring, the two diamonds appear to be the same size because they have the same diameter.
4. How does diamond carat weight affect price?
When a diamond weighing more than 100 carats is discovered, it immediately becomes big news in the diamond industry. One reason it’s so noteworthy is that the larger the diamond, the rarer it is; and the rarer the diamond, the more valuable it is. The same rule applies to diamonds in engagement rings. There are significantly more naturally occurring diamonds lighter than one carat than diamonds one carat or heavier. This is reflected in the price, too; due to their rarity, large diamonds are often so valuable that their price scales exponentially with weight rather than geometrically. In other words, a 1.00 carat diamond costs much more per carat than a 0.50 carat diamond. A 2.00 carat diamond also costs significantly more per carat than a 1.00 carat diamond.
5. Diamonds of certain carat weights will see a price jump
The difference in size between a 0.98 carat diamond and a 1.01 carat diamond is hard to tell, but some people prefer to have symbolic numbers, such as rounded numbers. The industry calls diamonds weighing 0.25 carats, 0.50 carats, 0.75 carats, 1.00 carats, and so on “popular sizes.” While you may not see many popular sizes, you should still be aware of them. The reason: Diamonds that are exactly or slightly heavier than a popular size are generally more expensive per carat than diamonds that are slightly lighter. So if you don’t need a symbolic rounded “weight,” you can save a little money by choosing a diamond that’s a few points lighter.
6. Carat weight and total carat weight are not the same thing
Many diamond engagement rings feature more than one diamond. A halo (a circle of diamonds or colorless gemstones surrounding the center stone) or side stones (one or more diamonds flanking the center stone) are common and popular features in engagement rings. While “carat weight” refers to the weight of a single stone, “total carat weight” (sometimes abbreviated “tcw”) describes the weight of all the diamonds in a ring with multiple stones. For example, an engagement ring with a 1.20 ct center diamond surrounded by a halo of 0.30 ct diamonds would have a total carat weight of 1.50 ct. Total carat weight affects the price of an engagement ring. However, assuming all stones are of equal quality, the main factors that affect price are the size of the center diamond and the size of each side stone. For example, this engagement ring features a 1.00 ct center diamond and two 0.15 ct side stones for a total carat weight of 1.30 ct. It will usually cost more than a ring with six equal quality side stones weighing 0.05 carats each, even if their total carat weight is the same. Likewise, an engagement ring with a 1.50 carat solitaire will cost more than an engagement ring with a total diamond weight of 1.50 carats.
You’ll also find that some engagement rings feature a center diamond and colored gemstone side stones (such as rubies, sapphires or emeralds). For rings with different types of gemstones, the weight of the gemstones is called the “total gem weight.”
Adding the total weight of the rubies (1.62 carats) to the total weight of the diamonds (1.44 carats), the total gemstone weight of this ring is 3.06 carats.
7. When to Use Price Per Carat to Compare Diamonds
If you are buying a loose diamond, you should compare it to at least one similar loose diamond. First, ask for the price per carat of your chosen diamond. For example, if a diamond sells for $15,000 and weighs 1.50 carats, its price per carat is $10,000, which is calculated by dividing the diamond’s price by its carat weight. In this example: $15,000 ÷ 1.50 = 10,000. A 1.60 carat diamond with the same total price would cost $9,375 per carat (15,000 ÷ 1.60). If you use the price per carat as a benchmark, make sure the diamond:
- Grading by the same laboratory. Some laboratories may use different standards or processes when grading diamonds.
- Same shape. Different shapes usually have different per-carat prices. For example, it is difficult to compare a 1.00 carat oval or pear-shaped diamond to a 1.00 carat round brilliant diamond.
- Have the same or nearly the same cut, color, and clarity grades. If you compare a 1.00 ct round brilliant cut diamond with an Excellent cut grade to a 1.00 ct round brilliant cut diamond with a Poor cut grade, the comparison will be skewed.
8. Bigger diamonds are not necessarily better.
If you have an unlimited budget for a diamond engagement ring, you can buy a stone that has outstanding color, clarity, cut and carat weight. However, most people have to prioritize the 4Cs and decide which C is the most important . Usually, it is not the carat weight that is the most important. You may want a diamond that will turn heads, a diamond that cannot be ignored. But a larger diamond does not necessarily have to be visually stunning. A diamond must have a lot of brightness, fire and sparkle to make people’s eyes light up and can’t help but admire it. These qualities are mainly determined by the cut of the diamond, which also determines whether the diamond can produce small sparks. No matter how big the diamond is, you usually can’t see fire in a round brilliant diamond with a cut grade of “Fair” or “Poor”. For emerald cut diamonds , using carat weight as the main criteria for purchasing a diamond is also problematic. These elegant and beautiful stones have long rectangular facets that cannot hide inclusions. In addition, the faceted step cut style has less sparkle, which masks the lower color grade. Therefore, clarity and color grade are particularly important. An emerald cut diamond that is larger but has a lower clarity or color grade may look unappealing. These are two examples of why carat weight should not be the only criterion. When buying a diamond, it is best to consider all aspects of the 4Cs.
9. To confirm the diamond’s carat weight, please obtain a GIA grading report.
A diamond engagement ring is a significant emotional and financial investment—it represents your love and commitment. A GIA diamond grading report can ensure that the carat weight of the diamond you are selecting is accurate.
