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 favor of getting the biggest possible stone they have budgeted for. Although the carat weight 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.

How much does carat weight affect cost?

The effect of all the different properties of diamonds 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.