Your Biggest Questions about Diamond Carat Size, Answered

When it comes to weddings, size is always fodder for anxiety. What scale of reception can we afford? How many groomsmen and bridesmaids can we have without destroying friendships? (At least you probably don't have to worry about any reveals on the wedding night, like our grandparents did.) And because you've found Four Mine, you don't have to worry about diamond carat size, either.

In popular culture, the Size of the Rock has achieved a mythical stature as a status signifier, at least since Elizabeth Taylor and Richard Burton flaunted Liz's ginormous square ring in the early '70s. In movies and TV, new fianceés and other ring-bearers brag about diamond carat size whenever possible, waggling a heavily adorned finger at envious peers. (And you see the same thing done on social media with celebrity engagement rings.)

Probably not a shocker: This kind of shorthand is misleading. Diamond carat size is different than the physical size of a diamond, and neither one is an absolute guarantee of quality. Read on for everything you need to know when selecting the best engagement ring, when it comes to diamond carat size. (And check out our comprehensive diamond size chart after.)



How do you size a diamond?

Diamonds can be measured in both carat weight and millimeter. The millimeter tells you the true size of the diamond. Diamonds are most often evaluated and purchased in terms of carat weight, but it's important to consider millimeter measurements as well.


diamond carat size man cutting stone

Two diamonds of the same carat weight can have different faceting, and one can look larger than the other. If you're looking for a diamond that looks larger face-up, consider getting a fancy-shape diamond. Often, shapes like emerald, oval and pear can look larger than their round counterparts when viewed from the side.



What does diamond carat mean? Is a carat a weight or a size?

The carat is the standard unit of measurement for diamonds. Although most people think of a carat as a size, it is actually a weight. One carat is equivalent to 0.2 grams. Two diamonds of equal carat weight can have very different price tags, depending on qualities like cut, color and clarity. Gemstones are labeled by their weight, not size, because a round stone that weighs as much as a princess cut diamond sacrificed more of its rough diamond formation to become a finished engagement ring.



What is the size of a 1-carat diamond? A 2-carat diamond?

A 1-carat diamond is about 0.6mm. A 2-carat diamond is approximately 0.8mm.


diamond carat size gemologist weighing stone

How can you be sure of the carat size?

Carat weight and millimeter measurements can always be found on the GIA certificate of the diamond. They’re determined through a process called diamond certification. The certificate, also known as a diamond report, is issued by an independent gemology laboratory and notes the diamond's weight, measurements, and grades for the cut, color and clarity. Only the carat weight and measurement is factual; the rest is a subjective opinion of the gemologist based on their training.



How do you measure a diamond in MM?

A diamond is measured in millimeters by its view from above — by multiplying the length by the width. To the naked eye, a diamond of a taller shape — such as oval, pear or marquise — may look larger than a flat diamond, but that's not necessarily so.


diamond carat size graphic comparing sizes

And two diamonds of the same shape and carat weight can look different in size. That's because of cut proportions: A deeply cut diamond holds a larger percentage of weight in its depth, so it will have a smaller diameter than a well-cut diamond. A well-cut diamond may have a lower carat weight than a deeply cut diamond, yet still have a larger diameter. (If that all seems confusing, fear not. We have expert gemologists on staff to help you through this details to find the best diamond for you and your budget.)



What is the best carat diamond?

The average carat weight of an engagement ring is 0.9 carats. The average retail price of a 1-carat ring is about $1,200, but that depends on where you live and where you're looking. But remember, the carat is only one of the four C's of diamonds you should consider when selecting a ring — clarity, cut and color are also important characteristics of a quality diamond.

Fun fact: The largest diamond ever sold was a 118-carat egg-sized diamond that fetched $30.6 million at a Sotheby's auction in Hong Kong. So you have plenty to aspire to.


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