The Ultimate Diamond Carat Size Guide

New to the world of wedding ring shopping? Find out everything you need to know with our diamond carat size guide from Zola.

By Jennifer Prince

ruler to measure rings
Photo by Unsplash

Out of all the proverbial fish in the sea, you found the one—your person. The human you want to be with for the rest of your life. Congrats! Just like people come in all shapes and sizes, so do diamonds. Thankfully gemstones are a bit easier to figure out. Although we can’t demystify your partner, our diamond carat size guide can help you choose the perfect diamond engagement ring.

Beyond the Diamond Carat Chart

Before getting into the nitty-gritty of diamond weight comparisons, it’s essential to familiarize yourself with a few diamond facts not generally included on a diamond weight chart.

Diamond Carat Size Guide Photo Credit // Unsplash

Weight Is Not Equal to Diamond Carat Size.

Yes, size matters. When someone gets engaged, we immediately want to see that stunner on their finger. The first thing we tend to notice is the size of the diamond engagement ring, and then our mind focuses on the shape, sparkle, and details surrounding the stone. Even though the tendency is to interchange the terms “size” and “carat,” they are vastly different.

The term carat refers to the weight of the stone, measured in one of two ways. Using metric terms, one carat equals 0.2 grams or 200 micrograms, also equal to 100 points. So, a two-carat oval diamond ring will equal 0.4 grams or 400 points. Above all, a diamond weight calculator measures carats, but doesn’t necessarily indicate how large a stone will look.

A One-carat Diamond Price Varies Depending on Other Factors.

Of course, with great size comes great expenditure. The total weight of the stone is the determinant of price. Diamond market price charts also vary annually, as the cost of diamonds fluctuates from year to year.

Other factors—such as diamond cut, shape, color, and clarity (also known as “the four Cs” for diamonds)—impact the worth. A one-carat diamond price isn’t the same for each gemstone across the board. For example, a blemish-free, one-carat gem will be more expensive than the same size stone filled with imperfections. Although there are diamond price per carat calculators available, the gemstone must be considered in its entirety. In short, bigger doesn’t always equal better.

Diamond Carat Price Rises Exponentially With the Stone’s Weight.

When you spy that perfect 1.5-carat oval diamond ring in the case, don’t assume that a three-carat diamond will be twice the price. As the weight of a single diamond increases, so does the price per carat. Likewise, a one-carat ring won’t cost the same as four quarter-carat stones.

Thus, it’s important to note that carat weight is not the same as total carat weight. Many rings have side stones used to calculate the total carat weight of the diamond engagement ring itself. For example, a multi-stone ring may contain a half-carat center stone and two quarter-carat side stones. Although the total carat weight of the ring is one-carat, the value is not the same as a one-carat solitaire.

Things That Factor Into Diamond Carat Size

Not everything can be solved by consulting a diamond size chart. Millimeter (mm) sizing measures across the surface of a diamond and doesn’t take into account its depth. Consequently, there are other factors to consider, such as shape and how the facets are cut.

Diamond Shape

If you’re on the hunt for oval engagement rings, it’s best not to consult a marquise diamond size chart. Although their forms are somewhat similar, the shape of your gemstone will significantly affect the weight. So, instead of comparing apples to oranges, it’s best to use the same shape stone when factoring in diamond carat size comparisons.

So, how big is a half-carat diamond? To know how it will look on your hand, consider your favorite shapes. Diamond size charts are generally specific to the shape of the stone. Indeed, you want to determine the best carat size for the width of your fingers.

Diamond Cut

If you think that a diamond’s cut and shape are the same, think again. What you see from the top is the shape, and the geometry is the cut. Due to nature, several factors—such as imperfections and light reflection—must be taken into account when carving a stone.

If an area has several inclusions—or flaws—a gemstone cutter may cut the stone into the shape of a heart to better hide imperfections. In contrast, a less included area is ideal for a flawless, emerald cut diamond. Size charts often don’t take the stone’s cut into account, and the depth of the gem is also a factor. For example, a shallow cut 1.5-carat oval diamond ring may appear the same size as a two-carat oval diamond ring with a deeper cut.

Diamond Carat Size Guide

Diamond Size Comparison by Carat Weight

Gemstones are three-dimensional. Therefore, you can’t simply add the width of two half-carat stones to get the dimensions for a full carat. For reference, a US nickel is almost two mm thick—1.95 mm, to be exact.

  • 0.25 carat = 4.1 mm
  • .5 carat = 5.1 mm
  • 1 carat = 6.4 mm
  • 1.5 carat = 7.4 mm
  • 2 carat = 8.1 mm
  • 3 carat = 9.3 mm
  • 4 carat = 10.2 mm
  • 5 carat = 11 mm
Diamond Carat Size Guide Photo Credit // Unsplash

Diamond Carat Size Comparison by Shape

The slimming, little black dress is famous for a reason as it tricks the mind’s eye. That philosophy also works for diamonds. A long, thin marquise tends to look more substantial than a princess cut stone of the same weight. For reference, these are the approximate dimensions for one-carat stones.

  • Marquise = 10.5x5 mm
  • Pear = 8.5x5.5 mm
  • Oval = 8x5.5 mm
  • Emerald = 6.5x5 mm
  • Heart = 6.7 mm
  • Round = 6.4 mm round
  • Cushion = 6.5x5.5 mm
  • Asscher = 5.5 mm square
  • Princess = 5.5 mm square
  • Radiant = 6x5.5 mm

A Final Piece of Advice

We can chat all day about the weight, shape, and clarity of your diamond, and so can your jewelry salesperson. But it’s very important to gert documentation to go with your gemstone. Associations such as the Gemological Institute of America (GIA) and American Gem Society (AGS) have standards and grading systems for diamonds.

An engagement ring is a significant purchase. The proper documentation not only gives you confidence in your purchase, but is also vital for insurance purchases. If your diamond ring gets lost or stolen, your certificate can help replace it quickly.

A diamond carat size guide wouldn’t be complete without noting the nuances that characterize the gemstone industry. But no matter your choice of stone, rest assured that it will represent your love and commitment to your perfect catch.