Key Points

  • Carat is specifically a measure of a diamond's weight, and by itself may not accurately reflect a diamond's size.

  • We tend to evaluate diamond size by viewing it from the top because that is how diamonds are presented to us when set into a ring.

  • To understand diamond size, carat weight should be considered in conjunction with two other criteria:
    • Distance in millimeters across the top of the diamond.
    • Diamond's cut grade.

Diamond Carat Size Chart

This print out illustrates how diamonds of different carat weights and shapes will appear when viewed from the top down.

Your diamond may differ from the printout in length/width ratio, table, and depth.

View Diamond Carat Size Chart
Diamond Carat Size Chart
(This document is a PDF file PDF and requires Adobe Acrobat Reader. If you do not have Acrobat Reader download it for free.)


As the name suggests, carat weight specifically refers to a diamond's weight. However, much as a person's weight does not necessarily correlate with height, carat weight, by itself, may not accurately reflect a diamond's size. To gain a precise understanding of diamond size, Blue Nile recommends considering carat weight with two other characteristics: 1) the distance across the top of the diamond measured in millimeters, and 2) the diamond's cut grade.

It is important to measure the distance across the top of the diamond as this is how we view a stone when set into a ring.

A diamond's cut grade should also be considered because, as we noted in the cut grade section, when a diamond is cut with the proper proportions, the maximum amount of light (or sparkle) is returned out of the top of the diamond. Thus, when a diamond is well cut, the light reflected out of the top makes it appear larger. In addition, much of the weight of a poorly cut diamond, for example, may be "hidden" in the base of the diamond, making the diamond appear smaller than its carat weight would imply.

It is therefore possible to have a diamond of a lower carat weight, but higher cut grade, that appears larger than a diamond with a larger carat weight, but poor cut.

Once you've selected your cut, colour, and clarity grade, it's easy to determine the carat weight of diamond that will fit within your budget.

Much as there are 100 pennies in a dollar, a one-carat diamond is comprised of 100 points. Hence, 50 points is equal to 1/2-carat, and so on.

This chart illustrates how diamonds of different carat weights look when set in a ring. Note that a 2-carat diamond does not appear to be twice the size of a 1-carat diamond when viewed from the top.

Choosing Diamond Size


Choose a carat weight
1/4
1/3
1/2
3/4
1
1 1/2
2
3
4
5

What Carat Weight Is Right For Me?

To choose the best carat weight of diamond, consider the size of her finger, the size of your setting, and your budget.

  • If a large carat weight is important to you, yet you're working within a strict budget, consider a diamond with a good cut, SI1-SI2 clarity, and an I or J colour grade.

  • Diamond prices jump at the full- and half-carat weights. Diamonds just below these weights cost significantly less, and, because carat weight is distributed across the entirety of the diamond, small size differences are almost impossible to detect.

  • Keep in mind that the smaller the finger, the larger the diamond will appear. A 1.5-carat diamond solitaire looks much larger on a size 4 finger than a size 8.

  • Not all settings will fit all diamond carats or shapes. If you have already selected a setting, check the diamond specifications of your ring or ask your Blue Nile Diamond and Jewellery Consultant (1-888-565-7641) for help. If you need a special jewellery piece created, Blue Nile can accommodate almost any request.

For even more help determining what size is best is to get an idea of what she is expecting. If you research carefully, you can get answers without even raising her suspicions. For ideas and suggestions on how to choose the right engagement ring, read our Engagement Ring Guide.

What are others buying?

The chart below reveals what types of diamonds other Blue Nile customers are selecting. Modify the cut, carat and price, and the chart will display what others are purchasing according to the various colour and clarity grades. By clicking on the percentages, our Diamond Search will generate a list of diamonds that correspond to those criteria.



Have a question?

Contact us by phone at 00353 1 899 1351 from Czech Republic, 0800 206 1160 from the United Kingdom, or 00353 1 899 1351 for all other EU countries or email at serviceuk@bluenile.co.uk. In addition, Live Chat is available during most business hours.

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