Diamond Depth Percentage Calculator

What Diamond Depth Percentage Means

Diamond depth percentage (depth %) is one of the core proportions used to describe a diamond’s cut. It is a ratio that tells you how tall the diamond is compared to how wide it is when viewed from the top. In plain terms, depth % answers a practical question: is this diamond “built shallow,” “built deep,” or roughly balanced relative to its face-up size?

Depth % matters because a diamond’s visible size and its light performance are both affected by the stone’s geometry. If a diamond is too deep, more of its carat weight can be hidden in the pavilion where you cannot see it face-up, which often reduces spread (how large it looks from the top). If a diamond is too shallow, it may look larger for its weight, but it can also risk losing light out of the bottom if angles are not well balanced. A Diamond Depth Percentage Calculator helps you interpret measurements consistently and connect depth to the tradeoffs that show up in real-world viewing.

Depth % Is a Ratio, Not a Measurement

A grading report typically lists measurements in millimeters, such as a round diamond showing a minimum and maximum diameter and a total depth, or a fancy shape showing length, width, and depth. Depth % converts those raw measurements into a standardized number that works across sizes. A 6.50 mm round diamond and a 7.00 mm round diamond can both be 61.5% depth, even though their depth in millimeters is different, because depth % compares depth to width.

This is also why you should avoid comparing depth in mm directly across diamonds of different sizes. Depth % is the correct comparison metric for screening. Depth in mm becomes useful when you want to visualize the stone’s profile or confirm that two diamonds with the same depth % still have meaningfully different physical depth because their face-up widths differ.

How Depth % Is Calculated for Round Diamonds

For a round diamond, the reference width is the average diameter at the girdle. Most reports provide two diameters because very few diamonds are perfectly round. If the report lists something like 6.45 – 6.48 × 3.98 mm, the average diameter is (6.45 + 6.48) ÷ 2. Depth % is then:

• Depth % = (total depth ÷ average diameter) × 100

Using average diameter makes the calculation more accurate and aligns with how depth % is typically presented on grading reports. This calculator follows that approach so your results match practical report interpretation.

How Depth % Is Calculated for Fancy Shapes

Fancy shapes (oval, cushion, emerald cut, radiant, pear, marquise, heart, and many more) do not have a single diameter. They have a length and a width. Different sources may reference width in different ways, which can make comparisons messy. For consistent screening, this calculator uses a simple reference:

• Reference face-up size = (length + width) ÷ 2
• Depth % = (total depth ÷ reference face-up size) × 100

This method creates a single comparable “face-up size” number and helps you compare depth across fancy stones without switching formulas. It is not meant to replace a lab’s exact internal methodology for every shape style, but it is extremely useful for consistent decision-making and lot screening.

Why Depth % Influences Spread and Face-Up Size

When buyers say a diamond “faces up small,” they are usually talking about spread: the visible width of the diamond relative to its carat weight. Deeper diamonds can hide more weight in the lower half. That weight is real, but it does not increase the face-up footprint as much as a shallower build would.

Spread is not automatically the most important goal, but it is a meaningful value consideration. Two diamonds with the same carat weight and similar clarity and color can have noticeably different face-up sizes. Depth % is one of the first numbers people use to predict that difference. This calculator’s “Spread Note” output is designed to translate depth % into a practical expectation: more spread potential (shallow), more hidden weight (deep), or balanced.

Depth % and Light Performance Are Connected, Not Identical

Depth % is a summary metric. It does not directly tell you the exact angles that make a diamond sparkle. Light performance is controlled by how the crown and pavilion angles work together to reflect and refract light back to the viewer. Depth % can hint at that geometry, but it cannot fully describe it.

For example, two round diamonds can both be 61.5% depth, but one might have a steeper pavilion and a smaller crown, while the other has a slightly different balance. Both can be attractive, but they may look different in brightness and fire. That is why a screening approach works best: use depth % to avoid extremes you do not want, then use angles, table %, and real-world images to confirm performance.

Depth % vs Table %: The Relationship Buyers Often Miss

Depth % and table % are frequently discussed together because they are quick to read on a report and often correlate with other geometry. Table % describes the top facet width relative to the diamond’s width. When the table gets larger, crown height can shrink, and the depth distribution between crown and pavilion can shift. When the table is smaller, the crown can become taller, which can change how fire appears.

None of these outcomes are guaranteed because cutting styles vary, but the key idea is simple: depth % gives you the vertical story; table % gives you the top-opening story. Together, they help you predict whether the diamond may lean bright, fiery, shallow-spready, or deep-weighted. This is why the Depth % tab includes an optional table % input: it lets the tool provide clearer context instead of treating depth as an isolated number.

How to Use the Depth % Calculator Tab

The Depth % Calculator tab is for the most common scenario: you have the diamond’s measurements in millimeters and want to compute depth %. Start by choosing round or fancy shape reference. Then enter the measurements and total depth:

• Round: enter min diameter, max diameter, and total depth.
• Fancy: enter length, width, and total depth.
• Optionally enter table % for a better context note.

The calculator outputs the reference width used, the depth %, an estimated range you can control with the range input, and readable signals that describe spread expectations and screening context. The range output is helpful when measurements are rounded or when you are working from approximate data.

How to Convert Depth % Into Depth in Millimeters

Sometimes you only have depth % but you want to visualize the physical profile in millimeters. This happens when browsing listings that provide table % and depth % but not a full measurement set, or when you are comparing two stones and want to translate proportions into physical dimensions.

The Depth (mm) tab solves this directly:

• Depth (mm) = (depth % ÷ 100) × reference width

For round diamonds, the reference width is the average diameter. For fancy shapes, the reference width is the average of length and width for consistent screening. If you enable the fancy output mode, you also get depth-to-length and depth-to-width ratios, which can help you compare stones that are similarly deep by one metric but not the other.

Practical Screening: What “Shallow,” “Balanced,” and “Deep” Can Suggest

Buyers often want a simple “good range,” but the truth is that depth % must be interpreted in context. Still, screening categories are useful because they tell you what to check next.

• Shallow builds may face up larger, but can be more sensitive to angle balance. If the pavilion is too shallow, light can leak through the bottom, reducing brightness.
• Balanced builds often produce a more typical spread and can be easier to match with well-proportioned angles, but you still need to validate the full proportion set.
• Deep builds can face up smaller and may hide weight. They can still be attractive and sometimes look “crisp” in pattern, but value-per-visible-size may be lower.

The Proportion Insights tab is designed for this step. It converts depth % (and optional table % plus angles for rounds) into a readable checklist: what the numbers suggest and what you should validate before you decide.

Why Fancy Shapes Need Extra Caution

Fancy shapes cover a wider variety of facet patterns than round brilliants. Two ovals can have similar depth % but different bow-tie intensity. Two cushions can be “chunky” or “crushed ice” with different light behavior at similar depth. Emerald cuts, which are step cuts, can show clarity more readily and have different performance priorities than brilliant cuts.

Depth % is still useful, but it is best treated as a consistency metric and a spread indicator rather than a final performance predictor. For fancy shapes, in-person viewing, videos, and clear face-up imagery often matter even more than for rounds.

Depth % and Setting Considerations

Depth in millimeters is not just a performance topic. It also affects how a diamond sits in a setting. Very deep stones can require a taller setting to accommodate the pavilion, which can change comfort and profile. Shallow stones might sit lower, but you still need to ensure that the culet and pavilion are protected and not exposed.

If you are designing a ring, converting depth % to depth in mm can help you communicate with a jeweler about practical fit. This is especially useful for certain fancy shapes where the pavilion depth can influence how the stone is mounted and how much light can enter.

Lot Totals for Inventory and Consistency Checks

If you are working with multiple diamonds, depth % becomes a powerful consistency signal. The Lot / Batch Totals tab estimates the depth (mm) for an average stone using an average reference width and an average depth %. It also totals the depth across the batch with an optional variability allowance. This can help you quickly see whether a lot trends deeper or shallower and whether it is likely to produce consistent face-up presentation.

For more precise results, group stones by shape and by similar size. A single “average” can hide meaningful differences in mixed lots, especially across fancy shapes with very different outlines.

How to Use Depth % When Buying a Diamond

Depth % is most valuable when it helps you narrow a shortlist. Start by using the Depth % tab to confirm the reported depth % matches the measurements you have (or to compute depth % when it is not provided). Then use the Insights tab to decide what to validate next:

• For rounds, review crown and pavilion angles together, not in isolation.
• Check table % in relation to depth % to predict whether the stone leans toward a particular look.
• Compare face-up size across stones at the same carat weight to understand spread tradeoffs.
• When possible, confirm performance with images or videos and observe the diamond under multiple lighting environments.

Depth % should not make the decision for you, but it can prevent common mistakes, like overpaying for hidden weight in an overly deep stone or choosing a shallow stone without confirming angles and light return.