Carat Weight

The size of a diamond has the biggest impact on its price. The metric carat, which equals 0.20 gram, is the standard unit of weight for diamonds and most other gems. If other factors are equal, the more a stone weighs, the more valuable it will be.

Here are several ways to express 1 carat:

1 ct.
200 milligrams
1/5 gram
100 points
4 grainer (not often used in retail environment)

It is very important not to mistake carat weight as referring to the dimensions of a diamond. It refers to weight only. Why the distinction? Because weight can hide in different parts of the stone. You can have a) well-cut, b) deep, or c) shallow Diamonds. Some may appear larger than others due to its cut.

Prices of diamonds are expressed in the trade as a price per carat. So when we say that the Carat Weight has the biggest impact on the price of the stone, we refer to the unit price per carat, not just the overall price of the whole stone.

Example 1:
Diamond "A" = 0.25 carats and costs $1,000 per carat. $1,000 x 0.25 = $250/stone.
Diamond "B" = 0.50 carats and costs $1,250 per carat. $1,250 x 0.50 = $625/stone.

It is very common for people to disregard the other C's in favour of getting the biggest possible stone they have budgeted for. Here at diamondgrading.com, although SIZE DOES MATTER, we feel it is just as important for the quality of the stone to be high.

Some people may feel it is more impressive to wear a 2 carat diamond than a 1 carat diamond. But that's not necessarily true. A Ferrari may not be as big a car as an Oldsmobile, but most would consider it more impressive.

How "big" is a carat?
Many people would like to "understand" carat sizes in real terms. Here's a simple trick to get an idea. Simply take a ruler, and look at the table below. These are some approximate, sample carat-weight to diameter-widths for popular sizes.

0.25 ct. - 4.1 mm  0.50 ct. - 5.2 mm 
0.75 ct. - 5.9 mm  1.00 ct. - 6.5 mm 

How much does "carat weight" affect cost?
The effect of all the different properties of Diamond on Cost is discussed in more detail in the Cost section. For carat weight, let's take a typical Diamond for an example, and see what happens when we take it through different carat weights.

A Diamond of G color and SI1 Clarity will be in one Category of prices when it is between 0.50 - 0.69 carats. When you take that same quality Diamond and increase the size to the next price category, which is the 0.70 - 0.89 carat range, the price increase will be approximately $1,100 per carat. Increase to the 0.90 - 0.99 carat range, and the price increase will be approximately another $800 per carat. Increase to 1.00 - 1.49 carat range, and the increase will be approximately another $800 per carat. If you increase to the 1.50 - 1.99 carat range, the price increase will be approximately $1,200 per carat.

Color
The color of a diamond has the second biggest impact on its price, after carat weight. Did you know that diamonds come in every color of the rainbow?

Grading color in the normal range involves deciding how closely a stone's bodycolor approaches colorlessness. Most diamonds have at least a trace of yellow or brown bodycolor. With the exception of some natural fancycolors, such as blue, pink, purple, or red, the colorless grade is the most valuable.

If a diamond does not have enough color to be called fancy, then it is graded in a scale of colors ranging from Colorless to Light Yellow, "D" through "Z". A diamond with a "D" color is considered to be colorless. If the color is more intense than "Z", it is considered fancy. A fancy yellow diamond fetches a higher price than a light yellow diamond.

The Laboratories only grade diamonds which are unmounted, or "loose", and they do so under special light. Once a loose diamond is mounted on a ring, even the trained professional cannot always tell the difference between, say a "D" color and an "E" or "F" color diamond!

Color  D E F G H I J K L M N O P Q R S T U V W X Y Z Fancy
Scale Colorless Near Colorless Faint Yellow Very Light Yellow <------Light Yellow------> Color

How much does "color" affect cost?

The effect of all the different properties of Diamond on Cost is discussed in more detail in the Cost section. For color, let's take a typical Diamond for an example, and see what happens when we take it through different color grades.

Let's start with a 1.00 carat Diamond of K color and VS1 Clarity. If you move up to an H color, you will pay approximately an extra $1,700 per carat. Move up to F color, the increase will be approximately $1,100 per carat. Improve the color to D and the increase will be approximately $900 per carat.

Clarity
The clarity of a diamond refers to how clear, or "clean" the diamond is. The more "clean" the diamond, the higher the price. Most diamonds have "imperfections" in them. The clarity scale is a measure of the severity of those imperfections or "inclusions" as it is known in the trade.

For example, a deep break in a diamond which is not that visible when you look at the stone face-up, could sometimes have a greater impact on the clarity of a stone, than a small black crystal which you can see very clearly face-up.

The following is the GIA Diamond clarity-scale:

FL-Flawless
These stones have no imperfections inside or on the outside of the stone under the magnification of a loupe of 10 power.

IF-Internally Flawless
These stones have no inclusions under a loupe with a 10 power magnification.

VVS1,VVS2-Very Very Slightly Imperfect
These stones have very small inclusions which are very  difficult to see under a loupe with a 10 power magnification.

VS1,VS2-Very Slightly Imperfect
These stones have small inclusions which are slightly difficult to difficult to see under a loupe with a 10 power magnification.

SI1,SI2-Slightly Imperfect
These stones have inclusions which are fairly easy to see under a loupe with a 10 power magnification, or visible to the naked eye.

I1,I2,I3-Imperfect
These stones have inclusions which range from eye visible to very easily seen to the naked eye.

Clarity FL
 IF
 VVS1
 VVS2
 VS1
 VS2
 SI1
 SI2
 I1
 I2
 I3
 
Scale
 Flawless-
Internally Flawless
 Very Very Slightly Imperfect
 Very Slightly Imperfect
 Slightly Imperfect
 Imperfect

SI3
Outside of the GIA Diamond clarity scale is a grade you may have seen called SI3. The Rap Sheet, which is a Trade Publication, honors the SI3 grade which is given out by EGL, the European Gemological Laboratory. It is described as a split between the SI2 and I1 clarity grade.

How much does "clarity" affect cost?
The effect of all the different properties of Diamond on Cost is discussed in more detail in the Cost section. For clarity, let's take a typical Diamond for an example, and see what happens when we take it through different clarity grades.

Let's start with a 1.00 carat Diamond of G color and SI1 Clarity. If you move up to a VS1, you will pay approximately an extra $1000 per carat. Move up to VVS1, the increase will be approximately $700 per carat. Improve the clarity to IF and the increase will be approximately $700 per carat.

Cut
The cut of a Diamond is the only property which is totally dependent on man. Although often overlooked, cut is actually one of the most important aspects to consider when choosing your diamond. A Diamond cutter analyzes the rough diamond, and has to determine how to extract the most beauty and most profit out of the rough stone.

Cut refers to not only the shape of the diamonds, but its proportions and finish, factors which determine the sparkle of the diamond.

It is possible to take the same stone, and depending on which method the cutter decides to use, to either cut it into the most beautiful stone it can be despite heavy weight loss and perhaps lower monetary value. Or else, he can cut a stone to its maximum weight and monetary value, but lose some "brilliance" and "sparkle"!

You see, even if you have two equal polished diamonds, both the same carat size, both the same color, both the same clarity, they may look completely different. How? There are many different shapes, and facets in a diamond. The weight can be distributed in different parts of the stone.

The goal in terms of extracting the greatest beauty from a Diamond, is to have light enter a Diamond, disperse the light as it bounces inside the Diamond, thereby producing the different colors and sparkly effect, and finally returning as much light to the eye as possible.

According to conventional wisdom, the proportions shown at the top of this page are the best for maximum light return. The 2-dimensional illustration below shows the theoretical path a ray of light will take through an ideal-cut Diamond. . As you can see, the rays of light entering the Diamond, reflect back to the eye. But it is possible for a diamond cutter to extract more weight out of the diamond by increasing the diameter of the stone. This will make the stone too shallow, and light may escape from the side of the stone, as shown here... or leak out of the bottom of the stone, like here... Another side-effect of this cut, is that it makes the stone appear larger. Don't be fooled by this. The fact that it appears larger than it is does not make it a better stone. If you compare a shallow stone to a well-cut stone, you will see the difference in how the well-cut stone "lights up".

By the same token, it is common to see the opposite problem. A stone which is cut too deep will "leak out light" in much the same way as the shallow stone. Here are two illustrations . . .
1)  and 2) .

This is not to say that a shallow or deep stone is a sign of a poor, or "low-quality" diamond cutter. Sometimes the shape of the rough diamond makes it impractical to cut a stone closer to "ideal" proportions without losing significant weight. But it is important to note the "light leakage" which will result from this cut. 

I hope this guide was helpful.