Carat Weight

Ruby

Carat Weight

Weight is an important quality of ruby value. Often the larger the stone, the more valuable it is, as larger stones more rare. However, it is important to remember that qualities such as color and saturation are also very important in determining a stone's value.

The English word carat come from the Greek keration ('little horn'), referring to the shape of the seedpods of the carob tree. These seeds are small and uniform in weight; therefore, they were a standard for weighing gemstones in early times.

Around 1920, the metric carat was adopted as an international standard. One carat equals a fifth of a gram (0.20 gram), or five carats to the gram.

Tavernier's Law

Generally, as a gemstone's carat weight increases, so does the price per carat. A fun way to look at stone values is the following: since the late 14th century there has been a law for diamonds that is known as the 'Indian Law' or 'Tavernier's Law':

Wt² x C = Price per Stone

The following shows how the price of a gemstone might increase with this formula applied to a $1000 a carat base price.

Weight
Total Stone Price
1ct
$1000
2ct
$4000
3ct
$9000
4ct
$16,000
5ct
$25,000
10ct
$100,000

However, in the real world, pricing is not this simple. Other qualities such as color or clarity affect the price of the stone. With colored gemstones, this carat law is even more muddled and unrealistic. A high quality ruby of three carats may be more valuable and rarer than a ruby of over 200 carats, as huge rubies are common, but full of serious inclusions. These giant specimens are impossible to cut into fine stones because of their flaws; therefore, their value is very low.

Also, remember that size and weight are different. Size refers to the physical space or volume that a stone occupies, while weight refers to the gravitational pull of the object. For example, one cubic millimeter of ruby will be twice as heavy as one cubic millimeter of opal because the ruby’s specific gravity is twice that of opal.

Approximate Carat Weights for Calibrated Rubies

Calibrated Size Chart for Ovals:

Dimensions (in mm)
Carat Weight (in carats)
4x3
0.20-0.25
5x3
0.28-0.35
5x4
0.45-0.52
6x4
0.50-0.60
7x5
1.00-1.25
8x6
1.35-1.70
9x7
2.00-2.60
10x8
3.00-4.00

Calibrated Size Chart for Emerald Cut:

Dimensions (in mm)
Carat Weight (in carats)
5x3
0.32-0.40
6x4
0.65-0.75
7x5
1.10-1.30
8x6
1.40-1.70
9x7
1.90-2.40

Calibrated Size Chart for Rounds:

Dimensions (in mm)
Carat Weight (in carats)
1.5
0.02
2
0.04
2.5
0.08
3
0.15
3.5
0.21
4
0.36
4.5
0.48
5
0.65-0.68
5.5
0.70-0.85
6
1.00-1.20

Calibrated Size Chart for Marquise:

Dimensions (in mm)
Carat Weight (in carats)
4x2
0.10-0.15
5x2.5
0.18-0.23
5x3
0.23-0.29
6x3
0.29-0.35
7x3.5
0.48-0.55
8x4
0.68-0.79
4x3
0.18-0.23
5x3
0.27-0.32
5x4
0.35-0.43
6x4
0.49-0.57
7x5
0.85-1.00
8x6
1.35-1.60

Calibrated Size Chart for Squares:

Dimensions (in mm)
Carat Weight (in carats)
1.5
0.03
2
0.07
2.5
0.12-0.16
3
0.20-0.25
3.5
0.32-0.40
4
0.40-0.46
4.5
0.52-0.60

Calibrated Size Chart for Pears:

Dimensions (in mm)
Carat Weight (in carats)
4x3
0.18-0.22
5x3
0.22-0.28
5x4
0.35-0.43
6x4
0.49-0.57
7x5
0.85-1.00
8x6
1.25-1.50

Sapphire

Carat Weight

Weight is an important quality of sapphire value. Often the larger the stone, the more valuable it is, as larger stones more rare. However, it is important to remember that qualities such as color and saturation are also very important in determining a stone's value.

The English word carat come from the Greek keration ('little horn'), referring to the shape of the seedpods of the carob tree. These seeds are small and uniform in weight; therefore, they were a standard for weighing gemstones in early times.

Around 1920, the metric carat was adopted as an international standard. One carat equals a fifth of a gram (0.20 gram), or five carats to the gram.

Tavernier's Law

Generally, as a gemstone's carat weight increases, so does the price per carat. A fun way to look at stone values is the following: since the late 14th century there has been a law for diamonds that is known as the 'Indian Law' or 'Tavernier's Law':

Wt² x C = Price per Stone?

The following shows how the price of a gemstone might increase with this formula applied to a $1000 a carat base price.

Weight
Total Stone Price
1ct
$1000
2ct
$4000
3ct
$9000
4ct
$16,000
5ct
$25,000
10ct
$100,000

However, in the real world, pricing is not this simple. Other qualities such as color or clarity affect the price of the stone. With colored gemstones, this carat law is even more muddled and unrealistic. A high quality sapphire of three carats may be more valuable and rarer than a sapphire of over 200 carats, as huge sapphires are common, but full of serious inclusions. These giant specimens are impossible to cut into fine stones because of their flaws; therefore, their value is very low.

Also, remember that size and weight are different. Size refers to the physical space or volume that a stone occupies, while weight refers to the gravitational pull of the object. For example, one cubic millimeter of sapphire will be twice as heavy as one cubic millimeter of opal because the sapphire’s specific gravity is twice that of opal.

Approximate Carat Weights for Calibrated Sapphires

Calibrated Size Chart for Ovals:

Dimensions (in mm)
Carat Weight (in carats)
4x3
0.20-0.25
5x3
0.30-0.37
5x4
0.45-0.52
6x4
0.50-0.65
7x5
0.95-1.20
8x6
1.25-1.50
9x7
1.75-2.25
10x8
3.00-4.00

Calibrated Size Chart for Emerald Cut:

Dimensions (in mm)
Carat Weight (in carats)
5x3
0.35-0.43
6x4
0.65-0.78
7x5
1.10-1.30
8x6
1.50-1.80
9x7
2.00-2.50

Calibrated Size Chart for Rounds:

Dimensions (in mm)
Carat Weight (in carats)
1.5
0.02
2
0.045
2.5
0.1
3
0.17
3.5
0.26
4
0.36
4.5
0.48
5
0.65-0.68
5.5
0.70-0.85
6
1.00-1.20

Calibrated Size Chart for Marquise:

Dimensions (in mm)
Carat Weight (in carats)
4x2
0.10-0.15
5x2.5
0.18-0.23
5x3
0.23-0.29
6x3
0.29-0.35
7x3.5
0.48-0.55
8x4
0.68-0.79
4x3
0.18-0.23
5x3
0.27-0.32
5x4
0.35-0.43
6x4
0.49-0.57
7x5
0.85-1.00
8x6
1.35-1.60

Calibrated Size Chart for Squares:

Dimensions (in mm)
Carat Weight (in carats)
1.5
0.04
2.5
0.07-0.09
3
0.12-0.16
3.5
0.20-0.25
2
0.30-0.40
4
0.38-0.50
4.5
0.62-0.73

Calibrated Size Chart for Pears:

Dimensions (in mm)
Carat Weight (in carats)
4x3
0.18-0.22
5x3
0.22-0.28
5x4
0.35-0.43
6x4
0.49-0.57
7x5
0.85-1.00
8x6
1.25-1.50