Free Diamond Table Percentage Calculator
A diamond table percentage calculator divides the width of a diamond's flat top facet (the table) by its average girdle diameter to show table size as a percentage, then compares the result with common ranges for the stone's cut shape.
Enter the average diameter from a grading report, or the length and width and we'll average them. Ranges are general trade guidance, not a cut grade; lab standards vary.
Table percentage
Enter measurements and press Calculate, or load the sample diamond.
Your result
Common table ranges by shape
| Shape | Preferred | Acceptable |
|---|---|---|
| Round brilliant | 53–58% | 51–62% |
| Oval | 53–63% | 50–66% |
| Pear | 53–63% | 50–66% |
| Marquise | 53–63% | 50–66% |
| Heart | 53–63% | 50–66% |
| Cushion | 58–68% | 55–72% |
| Princess | 67–72% | 64–75% |
| Emerald | 61–69% | 58–72% |
| Asscher | 61–69% | 58–72% |
| Radiant | 61–69% | 58–72% |
General trade guidance compiled from common grading and retail references. GIA, IGI, AGS, and other labs use different standards, and only round brilliants receive a formal GIA cut grade. Table percentage alone does not determine cut quality.
How diamond table percentage is calculated
Table % = table diameter ÷ average girdle diameter × 100
- 1
Measure the table
The table is the large flat facet on top. Measure it across its widest point.
- 2
Get the average diameter
Use the report's average, or (length + width) ÷ 2. Both values must use the same unit.
- 3
Divide and multiply
Table ÷ average diameter × 100. The unit cancels out, so mm and inches give the same result.
- 4
Compare by shape
Check the result against the range for the shape, then review depth, angles, symmetry, and polish.
Assumptions: results are rounded to one decimal place; inputs must be positive, at most 100 mm (about 3.94 in), and give a table between 35% and 90%. Hand measurements are less precise than a lab scanner.
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Diamond table percentage FAQ
How do you calculate diamond table percentage?
Divide the table diameter by the average girdle diameter and multiply by 100. A 3.6 mm table on a 6.45 mm round diamond is 3.6 ÷ 6.45 × 100 = 55.8%. Both measurements must use the same unit.
What is the ideal table percentage for a round diamond?
Many guides prefer about 53% to 58% for a round brilliant, and stones from about 51% to 62% can still be well cut. The best table depends on how it works with the depth and angles, so check the full cut grade too.
Is a bigger diamond table better?
Not necessarily. A larger table can look brighter and bigger face-up, but it usually leaves a smaller crown and less fire. A smaller table can add fire but may look smaller. Balance matters more than size alone.
Does table percentage determine diamond cut quality?
No. Table percentage is one proportion among many. Depth percentage, crown and pavilion angles, girdle thickness, symmetry, and polish all affect performance, and labs such as GIA, IGI, and AGS weigh them differently.
Why does my grading report show a different table percentage?
Labs measure with optical scanners and may round differently. For elongated fancy shapes, many reports divide the table width by the stone's width rather than the average diameter, which gives a higher figure than this calculator.