Nine Things About Diamond Carat Weight You Need to Know (2024)

If you’re shopping for an engagement ring, you need to know about carat weight – the measurement of how much a diamond weighs. Carat weight is important because it helps determine a diamond’s price and reflects its rarity. We take a closer look.

In this blog, we cover:
What is carat weight?
How is carat weight measured?
Carat weight is not the same thing as diamond size
How diamond carat weight influences price
Diamond prices jump at certain carat weights
Carat weight and total carat weight are not the same thing
When to use per-carat price to compare diamonds
A bigger diamond doesn’t necessarily mean a better one
To be sure the carat weight of a diamond is accurate, get a GIA grading report

1. What is carat weight?

Carat weight (ct) is one of the 4Cs of diamond quality – the universal standard GIA created to describe the attributes that determine a diamond’s value. The other Cs are color, clarity and cut.

Diamonds are weighed in carats – the international unit of measurement for gem weight. One carat equals 1/5 of a gram (0.20 g).

Nine Things About Diamond Carat Weight You Need to Know (1)

The seeds in a carob pod are so uniform in size (averaging about 0.197 gram) that early gem traders used them as counterweights in their balance scales. “Carat” is derived from the original Greek for carob bean, keratien, which also means a small weight. Photo: Orasa Weldon/GIA

The metric carat is divided into 100 points – abbreviated pt. An easy way to remember this is to think of carats as dollars and points as pennies. They’re even written the same way: $1.54 means one dollar and 54 cents; 1.54 ct means one carat and 54 points.

Don’t confuse carat with karat. Karat is a unit of measure for the fineness of gold. It is abbreviated as “K” or “Kt.” (Note that in the United Kingdom, “carat” is used to describe both gem weight and the fineness of gold.)

2. How is carat weight measured?

Diamonds are typically weighed using an electronic micro-balance scale. At the GIA laboratory a diamond is weighed to the fifth decimal place (1.12345), or a hundred thousandths of a carat, to ensure maximum precision. In the trade, however, a diamond’s carat weight is usually stated to two decimal places (1.12), a hundredth of a carat. Using stricter rules than normal mathematical rounding, GIA rounds up the diamond’s weight only when the last digit in the thousandths place is a 9. For example, a diamond that weighs 1.128 ct would be rounded down to 1.12, while one that weighs 1.129 ct would be rounded up to 1.13. The weight rounded to the hundredths place is then recorded on the diamond grading report.

The takeaway: Since the price of diamonds is calculated by multiplying the carat weight by the price per carat, you want to make sure that the diamond you’re buying has been accurately weighed.You also want to make sure the diamond’s stated weight is given with two decimal points. Why? A 0.97 carat diamond is not equal to a one carat (1.00 ct) diamond, and its price should reflect the size difference, assuming both diamonds have comparable color, clarity and cut qualities.

3. Carat weight is not the same thing as diamond size

Equating carat weight and size seems like common sense, but it doesn’t always work. Different gem materials have different densities (mass per unit of volume), so two gems that have the same carat weight may actually have very different sizes. For example, ruby has a greater density than diamond, so a one carat ruby will look smaller than a one carat diamond.

What’s more, the way a gemstone is cut also affects its perceived size. A poorly cut round brilliant diamond may be too deep or have a girdle that is too thick. Extra weight can be hidden in or below the girdle. Once the diamond is set, you won’t see this “hidden” carat weight, so a poorly cut 1.20 ct diamond may appear to be the same size as a well-cut 1.00 ct diamond. You end up paying for added weight with no added benefit. This is where the diamond’s cut grade – more than its carat weight – becomes important.

The takeaway: You shouldn’t use carat weight alone to estimate a diamond’s size. If it is a round brilliant cut, look at the diamond’s cut grade – available on the GIA grading report – to make sure it is well cut, so you’re not paying for wasted weight.

Learn more about cut: GIA Diamond Cut Grade: Six Things You Need to Know.

Nine Things About Diamond Carat Weight You Need to Know (3)

The diamond on the right has a much thicker girdle, so it weighs more. The thicker girdle has no visual benefit, but the added weight will make the diamond more expensive than its counterpart on the left. Both diamonds will appear to be the same size when set in a ring because their diameters are the same. Photos: Maha Tannous/GIA

4. How diamond carat weight influences price

When a 100+ ct diamond is found, it makes news in the diamond trade. One reason it’s noteworthy is because the larger a diamond is, the rarer it is. And the rarer it is, the more valuable it becomes. The same rule holds true for diamonds in engagement rings. Nature produces far more diamonds smaller than a carat than diamonds that are a carat or larger. This is reflected in the price.

Because of their rarity, large diamonds command a premium – so much so that the difference in price isn’t geometric but exponential. In other words, a 1.00 ct diamond will cost much more per carat than a 0.50 ct diamond. A 2.00 ct diamond will have a much higher per-carat price than a 1.00 ct diamond.

5. Diamond prices jump at certain carat weights

The size difference between a 0.98 ct diamond and a 1.01 ct diamond is difficult to distinguish, but some people prefer symbolic numbers, like round ones. The trade calls such diamonds weighing 0.25 ct, 0.50 ct, 0.75 ct, 1.00 ct, etc., “magic sizes.” Although you may not see many diamonds that are magic sizes, you still should know about them. Here’s why: Diamonds that are at or just above a magic size are generally more expensive per carat than diamonds that weigh a little less. So if you can live without the symbolic “weight” of these round numbers, you could save some money by choosing a diamond that weighs a few points less.

Nine Things About Diamond Carat Weight You Need to Know (4)

The diamonds in this photo range from 0.75 ct to 1.01 ct, but – for most of these stones – it’s challenging to see which ones are larger. Photo: Maha Tannous/GIA

6. Carat weight and total carat weight are not the same thing

Many diamond engagement rings have more than one diamond. A halo (a ring of diamonds or colored gems around the center stone) or side stones (one or more stones set on either side of the center stone) are popular design styles commonly seen in engagement rings.

“Carat weight” refers to the weight of a single stone, “total carat weight” – sometimes abbreviated “tcw” – is used to describe the weight of all the diamonds in a multi-stone ring. For example, an engagement ring with a 1.20 ct center diamond surrounded by a 0.30 carat halo of diamonds would have a total carat weight of 1.50 carats.

Total carat weight will impact the price of the engagement ring. But the chief driver of price is the size of the center diamond, along with the size of the individual side stones, assuming all are the same quality.

For example, an engagement ring with a 1.00 ct center diamond with two .15 ct side stones has a total carat weight of 1.30 carats. It will typically cost more than a ring with the same diamond with six .05 ct side stones, even though the total carat weight is the same. Likewise, an engagement ring with a single diamond weighing 1.50 ct will cost significantly more than an engagement ring with a total diamond weight of 1.50 carats.

Nine Things About Diamond Carat Weight You Need to Know (5)

This 1.01 ct old European cut diamond has a halo of 0.91 carats of diamonds. The total carat weight is 1.92 carats. Courtesy: TrueFacet

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Six round diamonds weighing 0.12 carats flank a 2.12 ct center stone. The total carat weight of this engagement ring is 2.24 carats. Courtesy: EraGem.com

You’ll also find engagement rings with a center diamond and colored gem side stones like ruby, sapphire or emerald. The gem weight in a ring with different types of stones is called “total gem weight.

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When the total weight of the rubies, 1.62 carats, is added to the total weight of the diamonds, 1.44 carats, it gives this ring a total gem weight of 3.06 carats. Courtesy: EraGem.com

7. When to use per-carat price to compare diamonds

If you’re purchasing a loose diamond, you’ll want to compare it to one or more similar loose diamonds. First, ask for the per-carat price of the diamonds at hand. For example, a 1.50 ct diamond that costs $15,000 has a per-carat price of $10,000 – that is, you divide the cost of the diamond by its carat weight. In this example: $15,000 ÷ 1.50 = 10,000. A 1.60 ct diamond with the same total cost would have a per-carat price of $9,375 (15,000 ÷ 1.60).

If you’re using per-carat price as the benchmark, be sure that the diamonds:

  1. Were graded by the same laboratory. Some laboratories may use different standards or processes when grading diamonds.
  2. Have the same shape. The price per carat often varies depending on the shape. This makes it tricky to compare a 1.00 ct oval or pear to a 1.00 ct round brilliant, for example.
  3. Have identical or nearly identical cut, color and clarity grades. Your comparisons will be skewed 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.

Your best course is to make apples-to-apples comparisons when using per-carat price as the determining factor. Here’s more information on how to compare loose diamonds.

8. A bigger diamond doesn’t necessarily mean a better one

If you had an unlimited budget to buy a diamond engagement ring, you could purchase a stone that has exceptional color, clarity, cut and carat weight. However, most people will have to prioritize the 4Cs and decide which C is most important. Often, it isn’t carat weight.

You probably want a diamond that has turn-your-head sparkle – one that can’t be missed from across the room. But a larger diamond doesn’t guarantee visual pizzazz. A diamond has to have lots of brightness, fire and scintillation to elicit “oohs” and “aahs.” These qualities are determined primarily by the diamond’s cut, which is responsible for the miniature fireworks. You typically won’t see them in a round brilliant diamond with a “Fair” or “Poor” cut grade, no matter how large it is.

Carat weight as the main criterion for buying a diamond is also a problem for emerald cut diamonds. These elegant beauties have long rectangular facets that do not hide inclusions well. Also, the step cut style of faceting has less scintillation, which masks lower color grades. So, clarity and color grades are especially important. A large emerald cut diamond with a lower clarity or color grade may look unattractive.

These are just two examples of why carat weight shouldn’t be used as the only measuring stick. It’s best to consider all the 4Cs when purchasing a diamond.

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Inclusions and blemishes detract from the beauty of a diamond. Photo: Robert Spencer/GIA

9. To be sure the carat weight of a diamond is accurate, get a GIA grading report

A diamond engagement ring is a significant emotional and financial investment – one that represents your love and commitment. A GIA Diamond Grading Report ensures that the carat weight of the diamond you’re considering is accurate.

Nine Things About Diamond Carat Weight You Need to Know (9)

A GIA Diamond Grading Report gives you the information you need to buy a diamond with confidence.

Now that you know about carat weight, get even smarter by reading these tips on diamond color.

Nine Things About Diamond Carat Weight You Need to Know (2024)

FAQs

How do you guess the carat weight of a diamond? ›

The simplest and most popular method is to weigh the diamond in milligrams and then divide the weight by 0.2. The answer is equal to the diamond's weight in carat. For example, if the diamond weights at 0.1 gram or 100 milligrams, once it is divided by 0.2 it will equal 0.5.

How much does diamonds carat weigh? ›

Carat is the unit of measurement for the physical weight of diamonds. One carat equals 0.200 grams or 1/5 gram and is subdivided into 100 points. For comparison, in units more familiar in the United States, one carat equals 0.007 ounce avoirdupois. Which would require over 2,265 carats to equal 1 pound!

Why does carat weight matter? ›

A higher carat weight simply means that the diamond is rarer. If having a more valuable diamond is important to you, then a higher carat weight is better for you. Higher carat weight diamonds are often bigger and more brilliant, but the diamond shape and cut quality also determine this.

How to tell what carat a diamond is? ›

Calculating how many carats a diamond weighs is not difficult. First, determine how many grams the diamond weighs and then divide its weight in grams by 0.2 to find its carat weight. Here is an example: The diamond weighs 0.3 grams. Divide 0.3 grams by 0.2 and you will discover that the diamond weighs 1.50 carats.

How do you calculate carat weight? ›

How to calculate the carats of a diamond? Our tool uses the following formulas to calculate the total carat weight of the piece of diamond: Asscher = Length × Width × Depth × 0.0080 × (1 + GT) × (1 + WC); Baguette = Length × Width × Depth × 0.00915 × (1 + GT) × (1 + WC);

How can you tell if a diamond is real by its weight? ›

Check the Weight

Diamonds and diamond simulants have different weights at the same size. This is called density or specific gravity. Diamonds have a specific gravity (SG) of 3.52. Diamonds are much heavier than moissanite (SG 3.1-3.2), but lighter than white sapphire (SG 4.0) and cubic zirconia (SG: 5.5-6.0).

Which carat diamond is best? ›

A good carat size for an engagement ring is anything over 0.5 Carat. At 0.5 Carat, the diamond will be noticeable but not overpowering. At 1.0 Carat, the diamond is more eye-catching.

How much should I expect to pay for a 2 carat diamond? ›

On average, you can expect the cost of a 2 carat diamond to widely vary depending on its shape, cut quality, clarity, color, and whether it's a naturally mined or lab diamond. The varying cost can range from $5,000 to $50,000 or more.

How much is the 1 carat diamond worth? ›

On average, the retail price for one carat diamonds can be anywhere between $2,000 to $16,000, and between $8,000 to $72,000 for two carat diamonds . And of course, the retail price and the resale value of a diamond are very different things.

What is the most popular carat weight? ›

The range of 1.0 to 1.9 carats is by far the most popular, but there are noticeable peaks at the 0.70 – 0.79 range, the 0.90 – 0.99 range and the 1.50 – 1.59 range. It's great to see that people take our advice and go for a diamond that's slightly lighter or heavier than industry cutoff weights to get the best value.

What does carat stand for? ›

Precious stones are weighed in carats; a single carat is equal to 200 milligrams. Carat is also a variant spelling of karat, which measures the purity (but not the weight) of gold.

What two things are measured in carats? ›

A carat is a unit of weight used to measure the size of a gemstone such as a diamond. A karat is a measurement indicating the proportion of gold in an alloy out of 24 parts, so 18K gold is 18/24 parts gold. However, the use of carat (in place of karat) to indicate the fineness of gold is also considered acceptable.

Can you visually tell if a diamond is real? ›

The way that diamonds reflect light is unique: the inside of a real diamond should sparkle gray and white while the outside should reflect a rainbow of colors onto other surfaces. A fake diamond, on the other hand, will have rainbow colors that you can see inside the diamond as well.

What is a diamond 💎? ›

diamond, a mineral composed of pure carbon. It is the hardest naturally occurring substance known; it is also the most popular gemstone. Because of their extreme hardness, diamonds have a number of important industrial applications.

How do carats work? ›

Carat denotes the weight of a diamond, not the size. Tiffany measures diamonds to 1/1000th of a carat; one carat equals . 20 grams. Tiffany diamonds are always cut to maximize beauty, not carat weight.

How to calculate visual carat weight? ›

Visual carat weight describes how large a diamond appears to the naked eye when viewed from above. A diamond's visual carat is calculated by measuring a diamond's surface area and comparing this measurement to the average surface areas of different carat sizes of the same diamond shape (round, cushion, etc).

How big is a .65 carat diamond? ›

5.79 x 5.79 x 3.49 mm

How much is 0.25 diamond worth? ›

What is a . 25 carat diamond worth? The value and price for a diamond of this size varies but is generally between £200 GBP and £310 GBP. Besides the grading of the diamond according to the three other Cs (cut, colour, and clarity), the fluctuation in market value also affects the price of a .

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