Diamond Carat

Diamond Carat is the most visual of the 4 C’s of diamonds. Carat is a weight measure for a diamond that is globally recognized. Not to be confused with karat (a measure of gold purity), a 1.00 carat or ct diamond weighs 0.20 grams. Contrary to popular belief, the carat is not the size of the diamond. The size of a diamond is measured in millimeters by length and width or in other words the diameter of the diamond. It typically takes about 250 tons of rock mining to produce just 1.00ct of diamond. That is why diamonds are rare and expensive.

Diamonds come in a variety of shapes and carat weights. A diamond cutter’s highest priority is to maximize carat weight of a diamond. The larger the diamond, the rarer and therefore more expensive it is. Diamonds are weighed with carat/gram scales very precisely to the 0.01ct. This measurement for diamond weight is universal and is used by countries around the world. Before the standardization of the metric carat in 1907, there were a variety of terms and measurements for the diamond. In the past carob seeds were used to measure carat weight as it was believed that the mass of each seed did not vary much. However, this was not completely accurate. Over time carat weight became standardized and has now also become a point of reference in when looking at the certificate of any diamond regardless of which institution certifies the diamond.

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Diamond Scale: The Range

Diamonds within each carat range have average millimeter sizes so you can approximate their visual size. Although each diamond is unique, these millimeter measurements are typically the norm, especially since diamonds today are cut with machines to ensure precision. To truly understand the diamond’s size, evaluate the measurements. Well cut Round diamonds have less depth than well cut fancy shaped diamonds (diamonds other than Round). For example a 1.00ct Round diamond will have ~6.40mm length/width vs a 1.00ct Princess diamond, which will have ~5.50mm. Fancy shapes tend to have more weight and less size. Thus round cut diamonds have a premium versus fancy shapes of the same carat weight. Visually, it is very difficult to discern the difference between diamonds that vary 5% - 10% in carat weight. For example, 0.95ct vs. 1.00ct. One additional factor that affects diamond size is the cut of the diamond. If a diamond is cut too deep, it may looks smaller than a lower carat diamond. When looking at carat weight and millimeter, it is also important to consider length to width ratios for each diamond shape. These will help you understand if a diamond is too shallow or too deep or if it has the correct and desired proportions for your shape. A deep 1.00 ct diamond can possibly look visually smaller than a 0.95ct shallow cut diamond. View our comprehensive diamond size and millimeter chart.

Diamond MM Chart

carat size chart with round diamonds showing the millimeter size of each popular diamond size

Carat Price Effect

Diamond pricing increases exponentially, not linearly, as diamond carat weight increases. Once a diamond hits it’s critical weight, the price bumps up. The critical weights are: 0.30ct, 0.40ct, 0.50ct, 0.70ct, 0.90ct 1.00ct, 1.50ct, 2.00ct, 3.00ct, 4.00ct, 5.00ct, 10.00ct. Diamond cutters will do everything they can to keep the diamond weight at or above each critical weight. Therefore, while it is often recommended to purchase 0.95ct diamonds vs. 1.00ct diamonds, it’s very difficult to find 0.95ct diamonds. Additionally, diamond manufacturers and suppliers know this “trick” and so they’ll price their diamonds accordingly.

The average diamond carat weight is 0.90ct. Consumers prefer Carat above the other C’s of diamonds because carat is the most visual C. When pricing diamonds, think about carat on one side and the other 3 C’s on the other side. In order to fit your diamond budget, as you increase carat, you may need to reduce the other C’s. Vice versa, if you increase the other C’s, you may need to decrease carat. Visually, a larger carat size will fill up more of the hand. However, if you do not maximize for cut and clarity, the reflection of light within the diamond will be hindered. This means that although you may get carat size, you will not get the sparkle from the diamond. Therefore, it is important to have a balance of all the 4 C's even if you are optimizing for carat weight for your engagement ring diamond.

Please see our diamond price estimator to understand the approximate pricing across a variety of diamond sizes, when combined with the other diamond attributes. Below you can also see different diamond carat sizes on hand to get an idea of the visual appearance of diamonds when worn within an engagement ring. This representation uses an average hand size to show the diamond carat weight. When shopping, be sure to consider her hand size as well as her finger size. These are important factors in determining which carat size you should be aiming for and which ring style to pair your diamond with. While the illustrations show a round diamond, keep in mind that most fancy diamond shapes like emerald, oval and pear will look larger on hand than a round diamond of the same carat weight. Learn more about the various diamond shapes to understand which is the best fit for her ring. Finally, also consider that once set within a ring, the diamond carat weight can look even larger depending on the engagement ring style that is chosen.

The easiest way to understand the difference in pricing is the diamond's price per carat. In the diamond industry, we look at the difference per carat. There, you'll see the exponential increase in value. Below is an example for a high quality G VS2 Excellent cut solitaire:

Carat Weight





Total Price

$ 4,000

$ 4,000

$ 8,000

$ 16,000

$ 38,000

$ 76,000

0.25ct round diamond on a hand for diamond sizing 0.50ct round diamond on a hand for diamond sizing 0.75ct round diamond on a hand for diamond sizing 1.00ct round diamond on a hand for diamond sizing 2.00ct round diamond on a hand for diamond sizing 3.00ct round diamond on a hand for diamond sizing 4.00ct round diamond on a hand for diamond sizing 5.00ct round diamond on a hand for diamond sizing
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Expert Buying Tips

  • Critical Weights: Buying diamonds below critical weights in which the diamond prices increase substantially. For example, consider buying 0.95ct vs 1.00ct. The price will increase as 1.00ct is a critical weight.

  • Choose diamonds that are cut very well. Those diamonds tend to have less depth and more spread. This means their measurements are larger making the diamond look visually larger than its carat weight.

  • Carat tends to be the most visual and popular of the 4 C's. Therefore you should hone in on the carat weight first. Remember though, carat weight isn't the only thing that matters - it must be balanced `