GCAL > 4C's Grading Tutorial > Carat



DIAMOND CARAT WEIGHT


In this section:


DIAMOND CARAT WEIGHT AND DIAMETER SIZE CHART

DIAMOND WEIGHT ESTIMATION FORMULAS

ROUND BRILLIANT
Average Diameter 2 x Depth x 0.0061 x Girdle Correction %

PRINCESS CUT
Length x Width x Depth x 0.0082 x Girdle Correction % x Weight Correction% = Approximate Estimated Carat Weight

ASSCHER STEP CUT
Length x Width x Depth x 0.0080 x Girdle Correction % x Weight Correction% = Approximate Estimated Carat Weight

CUSHION BRILLIANT
Length x Width x Depth x 0.00815 x Girdle Correction % x Weight Correction% = Approximate Estimated Carat Weight

HEART BRILLIANT
Length x Width x Depth x 0.0059 x Girdle Correction % x Weight Correction% = Approximate Estimated Carat Weight

TRILLION BRILLIANT
Length x Width x Depth x 0.0057 x Girdle Correction % x Weight Correction% = Approximate Estimated Carat Weight


MARQUISE BRILLIANT
Length x Width x Depth x 0.00565 x GC % x WC% (1½ : 1 ratio)
Length x Width x Depth x 0.0058 x GC % x WC% (2 : 1 ratio)
Length x Width x Depth x 0.00585 x GC% x WC% (2½ : 1 ratio)

PEAR BRILLIANT
Length x Width x Depth x 0.00615 x GC % x WC% (1¼ : 1 ratio)
Length x Width x Depth x 0.0060 x GC % x WC% (1½ : 1 ratio)
Length x Width x Depth x 0.00575 x GC% x WC% (2 : 1 ratio)

OVAL BRILLIANT
Length x Width x Depth x 0.00625 x GC % x WC% (1¼ : 1 ratio)
Length x Width x Depth x 0.0064 x GC % x WC% (1½ : 1 ratio)
Length x Width x Depth x 0.0067 x GC % x WC% (2 : 1 ratio)

EMERALD STEP CUT
Length x Width x Depth x 0.0092 x GC % x WC% (1½ : 1 ratio)
Length x Width x Depth x 0.010 x GC % x WC% (2 : 1 ratio)
Length x Width x Depth x 0.0106 x GC % x WC% (2½ : 1 ratio)

RADIANT BRILLIANT
Length x Width x Depth x 0.0081 x GC % x WC% (1 : 1 ratio)
Length x Width x Depth x 0.0084 x GC % x WC% (1½ : 1 ratio)



GIRDLE CORRECTION ADJUSTMENTS
Formulas above are for diamonds with THIN - MEDIUM girdles, add % below for thicker girdles
ROUND BRILLIANT (below 1.25cts):
Slightly Thick 2-3% • Thick 3-4% • Very Thick 6-9% • Extremely Thick 8-12%

ROUND BRILLIANT (above 1.25cts):
Slightly Thick 1-2% • Thick 2-3% • Very Thick 4-6% • Extremely Thick 6-8%

FANCY SHAPES
Slightly Thick 3-4% • Thick 5-7% • Very Thick 9-10% • Extremely Thick 11+%

WEIGHT CORRECTION ADJUSTMENTS

Squarish or High Shoulders
Pear +1% to +5%
Oval +1% to +10%

Wide or Fat Wings
Pear +1% to +5%
Marquise +1% to +10%
Large Culet
All Shapes +1% to +2%

Wide Corners
Emerald -1% to -5%
Radiant -1% to -5%
Pavilion Bulge
Emerald, Radiant & Trillion +1% to +15%

 


 Video: Watch How Diamonds are Weighed at GCAL


FREQUENTLY ASKED QUESTIONS

What is a carat?

Carat is the standard unit of weight measurement for gemstones.
One carat is equivalent to 200 milligrams.
One gram is equivalent to 5 carats.
One pound is equivalent to 2268.2 carats.
Carats are divided into 100 points, like cents to a dollar. A ½ carat diamond can also be described as a fifty- pointer

What is the difference between carat & karat?

In the US and Canada, Carat (abbreviated ct.) refers to the standard unit of weight used for all gemstones. Karat(abbreviated kt.) refers to the purity of gold. 24-karat gold is 99.9% gold, 18-karat gold is 75% pure gold and 14-karat is 58.5% pure gold.

Do carat weight and size mean the same thing?

Not exactly, although the terms are commonly used interchangeably. Carat is a unit of weight (mass) and size refers to dimensions measured in millimeters (mm).

The size of a 1-carat round brilliant diamond can range from approximately 6.20 mm to 6.80 mm in diameter, depending on the depth. A deep cut is smaller in diameter and a shallow cut is wider in diameter. A shallow cut makes a diamond look bigger (described as 'spread') but diamonds that are either too shallow or too deep sacrifice 'Cut' quality and therefore the brilliance.

Why are diamonds weighed in carats?

The word carat is derived from the carob bean, known for its uniform weight, which was historically used to balance scales when weighing gemstones. In 1907, the Fourth General Conference on Weights and Measures accepted the metric carat (200 mg) as a standardized unit of weight.

How are diamonds weighed?

Exact measurement of carat weight is important because slight difference in carat weight can have a large impact on price. GCAL weighs diamonds on precise electronic balances that are calibrated and verified daily according to ISO requirements. Carat weight is measured to a thousandth of a carat and then is rounded to a hundredth of a carat. If the thousandth of a carat is 9 then the weight is rounded up, otherwise, the weight is rounded down.

For example:
If a diamond weighs 0.708 carats, than GCAL rounds down to 0.70 carats.
If a diamond weighs 0.709 carats, than it is rounded up to 0.71 carats.

What is the largest diamond ever found?

The Cullinan diamond, discovered in 1905 in South Africa, weighed 3106.75 carats in its rough form. The largest faceted diamond cut from the Cullinan weighed 530.2 carats.

How carat weight affects value?

Carat weight is the simplest value factor to understand. The larger the diamond, the more it costs. More specifically, carat weight affects value in two ways:

Diamonds are priced on a per carat basis, which ranges greatly depending on the quality.

Calculate the price per carat to compare the cost of similar diamonds. Divide the selling price by the exact carat weight to determine the price per carat. For example, a 1.07 carat diamond that sells for $8,560 has a per carat price of $8,000 ($8,560/1.07 = $8,000).

Large diamonds are rarer than small diamonds; therefore, the price disproportionately increases as the carat weight increases. The cost of a 2-carat diamond is much greater than twice the cost of the same quality 1-carat diamond. A ring made of many small diamonds totaling 1-carat will most certainly cost less than a ring with a solitaire 1-carat diamond.


<< Previous:

Clarity Crading
Next >>

GCAL Lab Tour Video