Diamond Carat Size

Diamonds are sold by the carat (shown as cwt.), which is actually a unit of weight, though most think of a carat in terms of size. The word "carat" comes from the "carob" seed, the original unit of measure for diamond traders. Today, a carat is equal to exactly 0.2 grams (about the weight of a paper clip). Carat weight is unrelated to the similar sounding karat, which refers to gold's purity.
Two diamonds of equal carat weight can have very different costs based on other factors (such as cut, colour, and clarity). In understanding the importance of carat weight, know thy partner. If the recipient's heart is set on a certain size diamond, then carat weight will probably be the most important factor in your search until the desired size is attained. At that point, other criteria will take on more importance. Most women can tell you the carat weight and shape of their ideal diamond, and most men can tell you the price.
As the carat size of a diamond increases, the diamond's price increases at an increasing rate. Why? Because the larger the diamond, the more increasingly rare it is. Fewer than one in one million mined rough stones are large enough to produce a finished 1 carat diamond. So, as carat weight increases, you will typically pay more not only in total, but on a price-per-carat basis as well. Choose from our assortment of hand matched Diamond Stud Earrings set in 9k gold.


DIAMOND CARAT SIZE CHART

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.


Carat Weight

1.00

2.00

3.00

Approximate Size

https://www.lumeradiamonds.com/images/diamond-education/10.jpg

https://www.lumeradiamonds.com/images/diamond-education/20.jpg

https://www.lumeradiamonds.com/images/diamond-education/30.jpg

Diameter (mm)
Crown (mm2)

6.50
33.2

8.20
52.8

9.40
69.4

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.


DIAMOND CARAT SIZE COMPARISON

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.