Diamond Depth Percentage Calculator

Diamond Depth Percentage Calculator – Proportion-Based Cut Insight

This Diamond Depth Percentage Calculator helps you understand how your diamond’s basic proportions compare to common guideline ranges. By combining depth percentage, table percentage and shape-specific bands, the tool estimates a cut quality grade and explains whether the stone is likely to be too deep, too shallow or reasonably balanced for light performance and face-up size.

The calculator is built around two core measurements from lab reports: total depth and table size, both expressed in millimeters. It also uses minimum and maximum diameter to compute an average girdle diameter, which forms the basis of the depth % and table % formulas used in modern diamond grading.

The Depth Percentage Formula

Depth percentage compares the total height of the diamond to its face-up diameter. This is the key formula used in the calculator:

Here, TotalDepth is measured from the table to the culet in millimeters, and MinimumDiameter and MaximumDiameter are the smallest and largest girdle measurements. For very round stones these two diameters are almost equal, so AverageDiameter is essentially the face-up diameter.

If depth % is too high, the diamond is described as deep. More weight is hidden in the body of the stone and the face-up size can look small for the carat weight. If depth % is too low, the stone becomes shallow. It may look larger than average but can leak light through the pavilion, producing weaker brightness and contrast.

The Table Percentage Formula

Table percentage compares the width of the flat top facet to the average girdle diameter. The calculator uses the following expression:

TableSize is the diameter of the table facet in millimeters. Together, depth % and table % summarize how tall the diamond is and how big the top window is. Balanced combinations tend to support attractive brightness, fire and patterning, while extreme combinations can create glassy or dark looks.

Shape-Specific Guideline Ranges

Different shapes are cut with different facet designs, so their ideal proportion ranges are not identical. The calculator therefore uses shape-specific bands when interpreting your numbers.

• Round brilliant diamonds typically perform well with depth percentages around the low 60s and tables in the mid 50s.
• Princess cuts often have higher depth percentages, because their square outline and pavilion structure are different from rounds.
• Oval and cushion shapes can tolerate somewhat broader ranges due to their elongated outlines and varied facet styles.
• Emerald cuts, with large step facets, often look best in ranges that balance hall-of-mirrors reflections and face-up spread.

Inside the calculator, each shape is mapped to an ideal band and a slightly wider acceptable band for both depth % and table %. Values inside the ideal band support a higher cut grade, while values outside the wider band pull the grade down.

How The Cut Grade Is Estimated

The calculator uses the formulas for depth % and table %, then checks where each value falls relative to the guideline bands for the chosen shape. It classifies each metric and combines the classifications into an overall cut estimate.

The overall cut grade is then assigned using simple rules:

• Excellent: both depth % and table % are in the ideal bands for the shape.
• Very Good: one metric is ideal and the other is acceptable, or both are acceptable.
• Good: one metric is acceptable while the other is out of range.
• Fair: both metrics are out of range but not extremely so.
• Poor: at least one metric is far outside the wider band, indicating an extreme shallow or deep cut.

This approach emphasizes proportion balance. A diamond with a very strong depth % but an oversized table might still receive a moderate grade, because both metrics need to work together for strong light return.

Interpreting Deep, Shallow And Balanced Stones

Once the calculator has computed depth % and table %, it writes a plain-language note for each metric and an overall summary. Depth % and table % can be roughly translated as follows:

• Depth % below the shape’s lower guideline suggests a shallow cut. The stone may look larger for its weight but may leak light through the pavilion.
• Depth % above the shape’s upper guideline suggests a deep cut. The stone may hide weight in the body, appearing smaller than average for its carat weight.
• Table % significantly above the ideal band can make the diamond’s top look too open, reducing fire.
• Table % significantly below the ideal band can restrict the main window, sometimes making a stone appear darker.

Balanced stones, with both depth % and table % near the ideal bands, are more likely to support a strong cut grade, assuming crown and pavilion angles are also aligned with good light performance.

Why Carat Weight Is Optional In The Model

Carat weight does not enter directly into the depth % or table % formulas, since both are ratios of millimeter measurements. However, carat weight provides context for how the diamond should look face-up.

If the calculator reports a deep stone and you entered a relatively high carat weight, the overall note may highlight that the stone is likely to face up smaller than many diamonds with the same weight. For shallow stones, the note may acknowledge that the stone could look large for its weight but with potential trade-offs in light performance.

How To Use The Diamond Depth Percentage Calculator Step-By-Step

• Select your diamond shape, such as round brilliant, princess, oval, cushion or emerald cut.
• Enter the total depth from your laboratory report in millimeters.
• Enter minimum and maximum diameter from the report so the calculator can compute the average diameter.
• Enter the table size in millimeters; if your report lists only table percentage, you can convert it by using diameter × table % ÷ 100.
• Optionally enter carat weight to see notes about face-up size relative to weight.
• Run the calculation to see average diameter, depth %, table %, an estimated cut grade and a detailed interpretation of each metric.

Limitations And Best Practices

This tool focuses on basic proportion ratios. Full cut evaluation for diamonds also includes crown and pavilion angles, girdle thickness, culet size, symmetry, polish and pattern analysis. A laboratory cut grade from a major gemological lab is still the gold standard for grading. Use the calculator to understand proportions in a more intuitive way and to compare stones, but always consider the complete grading report and real-world viewing conditions before making a purchase decision.