close up of diamond ring
Diamonds,  Education

The 4C’s: Carat Weight

Carat weight might be the most obvious and straight-forward feature of diamond grading. The metric carat is simply the special unit of weight for diamonds and gemstones, and 1 carat equates to 0.200 gram or 0.007 ounce. Diamond grades are as precise as possible when it comes to carat weight, so let’s take a look at what this process entails and how to understand specific weights.

Carats & Points


Diamonds are often so tiny and light-weight that even the metric carat has to be subdivided to produce a precise measurement. That’s why you’ll usually see carat weight expressed as a decimal, like 0.25ct or 1.55ct, but you may also come across something called points. One point (pt) is equal to 0.1 carat (ct).

100 points = 1 carat

Points and decimals allow these tiny gems to be weighed super accurately, but you might also see carat weight expressed as a fraction, like 9/10ct or 3/8ct. However, it’s important to note that fractions are often less precise measurements. Typically, the fraction is actually referring to a range of weights rather than a specific measurement, so a diamond marked 9/10ct might actually weigh 0.90-0.95ct. If you come across a fraction weight, think of it as approximate rather than exact.

You can use the interactive tool below to see how carat weights compare!

How Diamonds are Weighed


Electronic scales are the most accurate tools for measuring gem weight. The best are so precise that they can weigh a diamond all the way down to .001ct (or 1/10 point)! Once an unset diamond is placed on the scale, its weight is read digitally in an instant. From there, the diamond’s weight might be recorded exactly as it is, or it may be rounded up or down to the nearest point (or 1/100ct).

For example, let’s say the scale reads 1.004ct. A diamond grader might record the weight as is, or they might take that number and round it down, labeling the diamond as 1.00ct. Similarly, a diamond which weighs 0.995ct might actually be rounded up, labeling it 1.00ct as well.

Rounding the weight might seem counterproductive or even imprecise, but even when rounded, diamond weights are accurate to 35 millionths of an ounce! Rest assured that rounding such tiny amounts up or down does not significantly impact a diamond’s final value.

How Weight Affects Value


For diamonds, pricing isn’t as straightforward as other things sold by weight. For example, let’s say the price of gold is $1000 per ounce. No matter how many ounces of gold you want to buy, you can just multiply your amount by the per ounce price. So, if you wanted a three ounce bar of gold, you could expect to pay $3000. This is not the case for diamonds!

When it comes to diamonds, value is all about rarity. So, let’s say you’re looking at a 0.50ct diamond priced at $1,500. Based on that price, you might assume that a 1.00ct diamond of comparable quality would cost you $3000. However, a 1.00ct diamond will actually cost up to 4 times more than a 0.50ct diamond!

Why? Because a 1.00ct diamond is much more rare than a 0.50ct diamond, and sizes over 1.00ct only get rarer!

Putting It All Together


close up of round cut diamond

When you’re on the hunt for a diamond, you’ll come across many different stones of the same carat weight and cut style, yet they’ll likely be priced differently. Let’s say you’re looking at two round brilliant 1.00ct diamonds, one priced at $3000 and the other $2000. If you’ve made it this far in our blog series, you’ll have a good idea why! Put simply, the higher priced diamond is more rare.

Now, based on that, you might assume that all comparable diamonds of the same weight will cost about the same—but they don’t! Believe it or not, a princess cut diamond with the same grade and weight as a round brilliant diamond will actually cost up to 25% less! That’s because all factors of the 4C’s come together to produce a diamond’s final value, and a princess cut simply costs less to produce. On the flip-side, that means you can get a larger princess cut diamond for the same price as a smaller round brilliant!

When it comes to diamond color, you might find that a 1.00ct natural blue diamond is much more expensive than a 1.00ct white diamond—even if the blue diamond is graded lower in cut and clarity! Why? Because it’s rare enough to find a naturally blue diamond at all—let alone one that weighs 1.00ct after being cut! By the same token, you might find a 1.00ct color-enhanced blue diamond that’s actually less expensive than a 1.00ct white diamond of the same clarity.

As you can see, each of the 4C’s can raise or lower a diamond’s value in unique ways, and now you know why! If you missed our other posts on clarity, color, and cut, check them out for more details on how each factor affects value.

If you still have questions, we’d love to help you further! Why not send us a message or pop into one of our stores?

You can also browse our extensive collection of diamonds and diamond jewelry right here on our website!

We hope to serve you soon!

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