Learning More on Diamond Carat Weight

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.

The 4Cs of Diamonds: Diamond Weight

Diamond weight is described using two terms: carat and point.   Carat is determined by measuring the distance across the top of diamond and is always listed in millimeters.  When measuring diamond weight it is important to factor in the cut grade.  In a well-cut diamond, the maximum amount of light enters and exits through the table making the diamond look larger than a poorly cut stone.

Like color and clarity, carat weight is a key factor in determining the value of a diamond. Diamond prices vary by carat weight increasing at the full and half-carat weights.  Diamonds just below these weight changes will be less costly and a majority of the time size is undetectable.  For example, a 1.00ct diamond will be in a different price point than a .98ct diamond, but the size will not be noticeable.   Also, since larger diamonds are more rare and costly than smaller diamonds a 1.00ct single diamond will cost much more than several smaller diamonds equaling a total carat weight of 1.00ct.

Diamond Measurements

Carat = 100 points or 200 milligrams

Point = 0.01 or one-hundredth of a carat

diamond weight chart

What carat weight is right for her?

There are several important factors to keep in mind when determining carat weight.

Price – diamond cut, we feel, is the most important of the 4Cs and you should always choose a well cut stone over weight.  If carat weight is important to you and you would like a larger stone, you have some flexibility in terms of price with color and clarity.

Finger size – a 1.00ct diamond will look much larger on someone with a size 4 finger than a size 8 finger.

Setting – certain settings can make a diamond appear larger than it actually is.  Our personal shoppers can help you determine which setting is right for you if you don’t already have something in mind.

Visit our education section for more on diamond weight

Can you compare one diamond to another?

With shape, weight, and cut all being equal you can compare like diamonds in terms of color and clarity. Diamonds of the same clarity can differ quite a bit. Let’s take a SI1 clarity diamond for example. When looking at the diamond’s plot or at the diamond directly through at 10x loupe the clarity characteristics can be quite different and you’ll want to choose the one that is most appealing to you. Unless flawless, all diamonds will have clarity characteristics and only you can decide what you’ll be happy looking at each day. When comparing like diamonds I suggest looking at no more than 3 at one time. Keep narrowing it down always keeping your top choice each time.

Use our diamond comparison tool to find the perfect stone.

Who came up with the 2 month salary rule for engagement rings?

If you’ve heard about the two month salary rule you have probably heard about the three month salary rule as well. Both rules are a myth and not a fact. There is no set dollar amount or percentage on how much you should spend on an engagement ring. This is an individual decision that you’ll need to make. Like any large purchase, we suggest establishing a budget first before you even begin to start looking. Once you’re budget is established and you have been provided with all the options available within that budget you’ll then be able to make an informed decision on which ring is right for you and your significant other.

While we’re talking about myths there is one other to bring up here. Bigger is better – so untrue. When shopping for diamonds, size is not the first thing you should look for. The cut of a stone should be your priority followed by color, clarity, and then weight.

Talk to one of our Graduate Gemologists who will guide you through the shopping process and help you find the perfect fit. By phone 1-800-979-1910 or by email customerservice@since1910.com.