Carat is the standard term used for the weight of a diamond and received its name from the seed of a carob tree.   The carob tree, which is native to the Mediterranean region, is an evergreen tree with an edible pod containing seeds.  The carob seeds were used by early diamond traders as counter weights on balancing scales as units of weight for small amounts of diamonds because of their consistent size.  The weight of the carob seed was 200 milligrams and the weight of a carat is exactly 200 milligrams or as it is know today, 0.2 grams.

Diamond Weight and Points

One of the first questions we’re usually asked is “how many carats is it?’ Many believe that the term carat represents the size of the diamond however; carat represents the weight of a diamond.

One carat is divided into 100 points.  So, for example, a quarter carat or 25 point diamond weights .25 carats (cts).   Diamonds weighing over one carat are expressed as carats and decimals.   They are measured to the hundred thousandths of a carat and rounded to a hundredth of a carat.   For example, a 1.25 diamond would be described as one point twenty five carats.

The cost of a diamond is not measured in weight alone.   Several diamonds of the same weight can be priced considerable different.  When calculating the cost of any diamond; clarity, cut, and color are major factors as well.

It is also important to understand that a 2 carat diamond will not look twice the size of a 1 carat diamond.   Since a diamond is three dimensional, the carat weight is dependent on both the diameter and depth.  A 1 carat ideally cut diamond averages approximately 6.45 millimeters in diameter and a 2 carat ideally cut diamond measures approximately 8.15 millimeters in diameter.  This is about 26% more in diameter than a 1 carat however; the price is about 4 ½ times greater.  As diamonds get larger in size they are also more rare and the price increases accordingly.

Weight of Round Brilliant Cut diamonds vs. their size.

Diamonds are always measured in millimeters.  Proportions for ideal cut diamonds shown below.

.25ct                        4.2mm

.50ct                        5.2mm

.75ct                        5.9mm

1.00ct                      6.5mm

1.25ct                      7.0mm

1.50ct                      7.5mm

1.75ct                      7.9mm

2.00ct                      8.2mm

2.50ct                      8.9mm

3.00ct                      9.4mm

4.00ct                    10.4mm

5.00ct                    11.2mm

How big of a diamond should I buy?

Carat weight is a personal preference and is a decision we can assist you with, but ultimately, you will need to decide what is most important to you.   For some, color and clarity are more important than size and customers will sacrifice size to obtain the best color and clarity within their budget.   Others will sacrifice on the color or clarity to get a larger diamond.

Regardless of your choice, as a member of the American Gem Society we will only sell you diamonds that meet our standards for color, cut, and clarity and display brilliantly.

Engagement Ring Budget

Prior to selecting a diamond, we recommend you set a budget.  By doing this first it will allow you to explore various combinations of color, clarity, and size that will not only meet your needs, but will keep you within your budget.

Remember, weight will not always increase the value of a diamond.  When a diamond is improperly cut it may reduce its brilliance.  A shallow cut diamond will have more surface area on the crown and will look bigger than one that is cut deep with more of its weight on the pavilion.  When a diamond is properly cut, regardless of weight, you get the most brilliance, fire, and scintillation which equals value.

Shop all Since 1910 loose diamonds and engagement rings to find the perfect one for you.


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