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Even though the price of a diamond increases exponentially with the carat weight, the actual size does not. The table below illustrates the typical size relationship between diamonds of increasing carat weights. Note that when carat weight triples (from 1 to 3 carats), perceived size (represented in the images below) roughly triples as well, however the diameter increases only 45% (from 6.50 to 9.40), and crown area (the surface area visible when the diamond is set) slightly more than doubles.


This is important to keep in mind when reviewing diamonds of any shape; a given increase in diameter will yield a larger increase in surface (crown) area and overall perceived size. While the third diamond above has a roughly 50% greater diameter than the first, it certainly appears more than 50% larger.


Size And Carat Weight Comparison
Two 1 ct. diamonds: The diamond on the left
has a deep cut and appears smaller from above.

When viewing diamonds on Lumera, check the measurements listed for each diamond to understand its size. The length and width will tell you exactly how large the diamond will appear when viewed from above.


Two diamonds of the same shape and carat weight may still appear different in size based on the cut proportions. A deeply cut diamond has a greater proportion of its total weight "hidden" in the depth, resulting in a smaller diameter than a well cut diamond. These differences are usually small, but noticable. A well cut diamond may even have a slightly lower carat weight than a deeply cut diamond, yet still have a larger diameter, making it appear larger in size.




Two diamonds of equal carat weight may also appear very different in size based on the shape of the diamond. For instance, a 1 carat marquise tends to appear larger than a 1 carat round. The chart below illustrates why. For each diamond, the chart shows the following:


  • Approximate size. The diamond images shown are a very close approximation of the actual size of a 1 carat excellent cut for each shape. Visually, the longer shapes (oval, marquise, pear, emerald) tend to appear larger to the eye than the round and square shapes.
  • Measurements (Length x Width). The measurements correspond to the shape shown above, and are typical for excellent cut diamonds of 1 carat weight.
  • Crown Area - The total surface area (mm2). The area gives the true size of the diamond face up (as it would appear when set in a ring). For example, while the oval diamond image appears larger than the round image, the actual surface area is the same for the two shapes, meaning the difference in size is one of perception, not reality. In contrast, the oval not only appears larger than the princess cut, it actually has a larger surface area (approximately 10% larger in this example), meaning the difference is not simply an illusion created by the elongated shape.



Remember that while the measurements below are typical, every diamond is unique.


Size Round 1 ct. Princess Cut 1 ct. Oval 1 ct. Marquise 1 ct. Pear 1 ct. Cushion 1 ct. Emerald 1 ct. Asscher 1 ct. Radiant 1 ct. Heart 1 ct.


































Crown 33.2 30.2 33.3 36.9 34.0 29.2 31.8 28.7 32.1 28.1


To see the actual size of each diamond shape at various carat weights, print the diamond carat size chart below:

Diamond Size Chart

A diamond's weight is measured in what is known as a "Carat", which is
a small unit of measurement equal to 200 milligrams. Carat weight is commonly expressed in points or fractions. There are 100 points per 1 carat. For example, 0.33 carats is usually expressed as 33 points, or 1/3 of a carat.

What does total carat weight mean?

The diamond total carat weight is a combined minimum carat weight of all the diamonds in a piece of jewelry. An example is if a pair of diamond stud earrings has a total diamond carat weight of ½ (.50) carat, each earring in this pair would have an individual carat weight of ¼ (.25) carat.

However, the actual diamond you purchase may weigh slightly more or less than the fractional weight specified. Because of this, the Federal Trade Commission has strict guidelines about the range of carat weight that a fraction can represent. The chart below shows the satisfactory ranges for carat weights expressed as fractions.
• 1/4 carat total weight may be 0.21 to 0.29 carats
• 1/3 carat total weight may be 0.30 to 0.36 carats
• 1/2 carat total weight may be 0.45 to 0.59 carats
• 3/4 carat total weight may be 0.70 to 0.84 carats
• 1 carat total weight may be 0.95 to 1.10 carats
• 1 1/4 carats total weight may be 1.20 to 1.29 carats
• 1 1/2 carats total weight may be 1.45 to 1.55 carats
• 2 carats total weight may be 1.95 to 2.05 carats

Why is carat weight important?

The carat weight of a diamond is one of the major factors affecting its price, along with cut, clarity and color.

Larger diamonds are rarer than small ones, so it’s value increases exponentially for higher carat weights.

How does carat weight affect diamond size?

As diamond carat size increases, the diameter and the depth of the diamond will also increase. This is the reason a 1 carat diamond approximately 6.5mm in diameter will not look twice as wide as a 1/2 carat diamond that is approximately 5mm in diameter.