That's right, you're going to have to weasel that micrometer away from the jeweler again. Which means you'll measure the diamond from the top of the table to the bottom of the culet. In order to get the depth, you'll measure the diamond from the top to the bottom. You'll do this by dividing the depth by the average girdle diameter. Now that you know how to calculate the table diameter, it's time to learn how to calculate total depth. While the AGS laboratory reports the average measurement to the third decimal point. But, you're still having fun learning about how it's done, right?Ĭonsequently, the table diameter is always rounded to the nearest whole percent by the GIA laboratory. Of course, the odds are that you'll probably never have calculate diamond proportions. This means that you will measure the diamond across the table at the widest point. In addition, you should know that the table diameters of fancy shaped diamonds are measured width wise. Then multiply the resulting quotient by one hundred. Simply divide the width of the table by the width of the stone. Regardless of that fact, here's how to calculate the table percentage of a fancy shaped diamond. Another problem with large table facets is that they reduce the dispersion of white light into color sparkle/fire. To demonstrate this just imagine the flat flash affect that overpowers light reflecting from a fish pond. You'll discover that a table facet which is too large tends to create an imbalance of scintillation. That means that a table diameter of 57.5% will appear as 58% on a GIA diamond grading report. Of course, you should know that the GIA rounds off table size to the nearest full percent. At the same time, the range of table diameter is 52.4 to 57.5% for an AGS-0 Ideal cut diamond. Generally speaking, most round brilliant cut diamonds have a table diameter between 55 and 65%. As a matter of fact, this is an idiosyncrasy of the labs that must be taken into account when evaluating diamond proportions. However, the AGS Laboratory will state the number as calculated above without rounding it off. The table percentage is always rounded to the nearest whole percent by the GIA Laboratory. Say what? Okay, here are the instructions in English: If the diamond measures 6.48 x 6.53 millimeters in diameter with a depth of 4.00 millimeters and its largest Table Diameter is 3.58 mm, then:Īverage Diameter = (6.48 + 6.53) ÷ 2 = 6.505 mm, which is the average outside diameter.ĭiamond Table Percentage = (3.58 table diameter divided by average outside diameter 6.505) = 0.5503458 × 100 = 55.03% which you would round off to a 55% table percentage. Then you will multiply the quotient by one hundred. Once you have taken these measurements, you will divide the longest table diameter by the average girdle diameter. Obviously, these lovely blue arrows will not exist to guide your way on actual diamonds. The idea is to measure the distance across the table from corner-to-corner.
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