This calculator can be used to estimate the approximate carat weight of a mounted diamond. Using a millimeter gauge, measure the length, width and depth of your stone. Jewelers and appraisers use digital gauges made specifically for measuring gemstones. Then input the measurements into the calculator below or use the formulas provided. Make adjustments for thick girdles or other shape variances (girdle correction % and weight correction %).
When you need to know a diamond’s exact weight, unmount it and weigh it on carat weight scale. If you’re making an important financial decision about your diamond, have a professional unmounted it and examined it when it is loose.
Diamond Carat Weight Estimation Calculator
Approximate Estimated Carat Weight = Length x Width x Depth x Shape (SF) x Girdle Correction Factor (GC) x Weight Correction Factor (WCF)
Approximate Estimated Carat Weight :
Diamond Carat Weight Estimation Formulas
Average Diameter 2 x Depth x 0.0061 x Girdle Correction %
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
Length x Width x Depth x 0.00815 x Girdle Correction % x Weight Correction% = Approximate Estimated Carat Weight
Length x Width x Depth x 0.0059 x Girdle Correction % x Weight Correction% = Approximate Estimated Carat Weight
Length x Width x Depth x 0.0057 x Girdle Correction % x Weight Correction% = Approximate Estimated Carat Weight
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)
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)
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)
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%
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%
All Shapes +1% to +2%
Emerald -1% to -5%
Radiant -1% to -5%
Emerald, Radiant & Trillion +1% to +15%
Diamond Color Grading involves determining how little or how much body color is in a diamond. The less body color, the higher the grade; the more body color, the lower the grade. This process is about deciding the amount of color, or more accurately, the lack of color in a diamond.
Using special set of comparison diamonds, known as ‘Masters’, gemologists find the closest color match from among the Masters to the stone being graded. Each ‘master’ is the highest of each grade.
Diamonds are studied in the table-down (or bottom-up) position to determine the quantity of color. This means that graders view the diamond's pavilion and culet rather than its table or crown. Why? To eliminate interfering brilliance and glare coming from the diamond's top.
Step-by-step Diamond Color Grading Procedure
What is the 'Master-Eye effect'?
This relates to the fact that most people have one eye that is stronger than the other, which creates a slight deviation in color perception. Essentially, a diamond appears darker in one position than another - even though the color is exactly the same. In effect, when a diamond is placed on the left of a Master Diamond it appears slightly darker than when placed to the right (it may be the opposite case with you, depending on which of your eyes is stronger). This is why we always position the diamond being graded (the unknown) to the right of the Master Diamond it is being compared to. Consistency in procedure results in accurate grades.
Color grading tips
Table down, face up, or umbrella position?
Although diamonds are usually positioned table down when color grading, the umbrella position is sometimes used. To position diamonds in the umbrella view, they should be on their side, slightly angled and diagonal to the grader's line of sight.
The umbrella position is very helpful to check and verify a grade decision, especially for fancy shapes, brownish colors, diamonds with dark inclusions, or uneven color distribution. Checking in this view is also useful for diamonds that are hazy or have limited transparency, strong fluorescence, or bruted girdles.
If the unknown diamond is close to, or the same color as, the Master Diamond when in the table down position, then check them in the umbrella view. If the unknown is better than the master in the umbrella position, than the final color grade will be the better color grade.
Diamond Clarity Grading involves determining the degree to which a diamond is free of blemishes and inclusions. It is the process of hunting down microscopic imperfections and rating them for difficulty of discovery. The more difficult it is to find inclusions under 10x magnification - using a binocular microscope - the higher the clarity grade. Once these specks are found, their number, size and location all play a role in deciding the final clarity grade.
Gemologists use an 11-grade scale - from 'FL' (Flawless), the highest, to 'I3', very noticeable inclusions - to grade clarity. Each grade down represents increased ease of detection. In short, grades stand for degrees of visibility.
The clarity grading environment
Grading a diamond in a laboratory environment is the ideal way to examine a diamond. Professional diamond laboratories, like GCAL, invest in high quality binocular microscopes, work in quiet darkened environments and have the advantage of examining perfectly clean loose diamonds. Gemologists and appraisers in the field often do not have these advantages.
Diamond clarity grades are always determined by what is visible at 10x magnification, not higher. Professional gemologists first examine the diamond with a microscope and then finalize the grade with a 10x loupe.
Clarity grading procedure
Here we are presenting grading procedures and principals we use every day in our laboratory.
The '4-position' method for deciding borderline clarity calls
After viewing the diamond in the microscope for all clarity characteristics, the grader will have an opinion of what the grade will be through the microscope view. This view is just used as a reference.
The final grade will ALWAYS be determined by the way the diamond appears through a 10x power loupe.
The 'theoretical grading' method
After locating all the grade setting inclusions, make the grade call that you think is correct. Then look at the grade setting inclusions again and mentally change what you are seeing. Then consider if your grade decision still makes sense. For example, mentally move the crystal from the center of the diamond to the edge, or change a crystal from dark to light, or eliminate some of the inclusions that contributed to the grade.
Consider how you would grade the clarity with the inclusions in a new location, etc. Can you justify your original decision?
How to grade transparent feathers and knots
How to Grade High Clarities (VVS2 and better)
Types of graining
Water grading is a technique that some graders prefer because it quickly removes surface dust and assists looking into the diamond.
Clarity grade descriptions
The following are examples of the types of inclusions and comments about each clarity grade.
No internal or external Inclusions at 10 power
No blemishes, surface graining, extra facets, polish lines, scratches or naturals at 10 power
Naturals totally confined to the girdle can be Flawless.
Excellent polish does not guarantee Flawless but a Flawless diamond has to have excellent polish.
No internal or external inclusions at 10 power
Any polish grade, symmetry grade, color grade or type of proportion can obtain an IF grade.
Extra facets, naturals, surface grain lines, polish lines, scratches, abrasions, and pits are acceptable.
'Polish' describes the quality of the facet surfaces and is related to the luster of a diamond. It can also be described as how free a diamond is from scratches. A high quality polish requires the diamond cutter to pay meticulous attention to the final stages of cutting.
Polish is graded as: poor, fair, good, very good and excellent. The majority of diamonds manufactured by modern cutting technology have at least good polish.
When judging a diamond’s polish quality, graders tend to start off with the grade of ‘good’ in their mind and then look for reasons to grade ‘very good’, ‘excellent’ or ‘fair’; but this is not the correct mentality. It is better to start off thinking ‘excellent’ and then find specific reasons to justify a lower grade. Remember, the diamond is innocent until proven guilty.
Polish grade descriptions
Each polish grade has a range. Here are examples of what you can expect to find for each grade:.
Grading external symmetry
External symmetry is a physical quality grade judged by a gemologist examining the exterior of a diamond under a microscope. It assesses the shape and alignment of facets. External symmetry is graded as: poor, fair, good, very good and excellent.
This should not be confused with optical symmetry, which is a grade of how well the diamond handles light as judged through digital imaging. It assesses the consistency of angles and alignment of facets by looking at the equality of light return.
As with judging a diamond's polish, when judging a diamond’s external symmetry graders tend to start off with the grade of ‘good’ in their mind and then look for reasons to grade 'very good', 'excellent' or 'fair'; but this is not the correct mentality. It is better to start off thinking 'excellent' and then find specific reasons to justify a lower grade. Remember, the diamond is innocent until proven guilty.
Here are some things to look for when grading a diamond’s external symmetry:
Judging girdle thickness
The widest part of a diamond, between the crown (top) and pavilion (bottom) is called the ‘girdle’. The thickness of the girdle is assessed as a range and described as: extremely thin, very thin, thin, medium, slightly thick, thick, very thick, and extremely thick.
Many graders are uncertain about assessing girdle thickness. Girdle thickness is important because it is part of the overall proportion grade and it is a factor in weight estimation of mounted diamonds.
Here are a few pointers:
Verifies the identification process
Verifies the 4C's quality grading
Illustrates the quality of cutting and proportions revealing the skill of the diamond cutter