When you’re choosing a diamond, it’s easy to focus on carat, colour or clarity. But there’s another detail that has just as much influence on how your diamond looks: its proportions.

Ratios and percentages may sound technical, but they quietly shape everything, the sparkle, the silhouette, and the way the stone feels on your hand. Understanding them helps you pick a diamond that doesn’t just shine, but feels like yours.

What Is a Diamond Ratio?

A diamond ratio is the relationship between the stone’s length and width:

Ratio=Length/Width

It’s simple maths, but the effect is anything but simple.

• Lower ratios (closer to 1.2–1.3 for ovals, for example) create a fuller, wider look.
  

• Higher ratios (1.4+) look more elongated and refined, giving the illusion of length and elegance.
  

Pro tip: If you’re considering an east–west setting (where the stone is set horizontally), lower ratios often look more balanced and bold.

Why Diamond Proportions Matter

Ratios define the shape, but diamond proportions,  table size, depth, crown angle, pavilion angle and overall height, define the brilliance.

When proportions are right:

• Light bounces beautifully within the stone.
  

• Sparkle, fire and brightness are maximised.
  

• The diamond appears lively, not dull.

When proportions are off (too deep or too shallow), light leaks away and even a high-grade diamond can lose its magic. That’s why gemmologists agree: cut quality impacts beauty more than any other factor.

How to Calculate Diamond Ratio

To calculate the length-to-width ratio, measure the stone at its longest point and divide it by the shortest point.

Example:

• Length: 7.0mm
  

• Width: 5.0mm
  

• Ratio = 1.40
  

• Ratios close to 1.0 = square (perfect for princess or cushion cuts).
  

• Higher ratios = rectangular or elongated (common in emeralds, ovals, and radiants).
  

This small number gives you instant insight into whether a stone will look broad and classic or slim and elegant.

The Key Diamond Proportion Factors

When jewellers talk about proportions, here’s what they mean:

• Table % – The size of the flat top facet compared to the diameter.
  

• Depth % – The diamond’s height compared to its width.
  

• Crown angle & pavilion angle – These angles decide how light bends and returns.
  

• Diamond height – The total depth from table (top) to culet (pointed base).
  

• Girdle thickness – The edge around the diamond, important for strength and symmetry.
  

Each of these measurements plays a role in whether the stone dazzles or disappoints.

Ideal Diamond Cut Proportions (Round Brilliant)

The round brilliant is the most precise diamond shape, and the only one graded across all aspects of cut: cut, polish, and symmetry. Engineered to maximize sparkle, it has been perfected over decades, with jewellers refining the proportions that consistently deliver brilliance.

Here are the best proportions for a round diamond:

Diamond Proportion Charts by Shape

Different diamond shapes shine at their best when cut to certain ratios. While there’s no single “right” answer, these guidelines offer a quick reference to the most popular cuts and their ideal proportions:

These ranges are guidelines, not rules. The best ratio is the one that appeals to your eye and feels right on your hand.

Choosing the Right Diamond Ratio for You

Numbers can guide you, but the right diamond ratio comes down to how it feels when you wear it. Do you want a stone that looks soft and vintage, or long and elegant? Do you prefer balance, or boldness?

There’s no single “best” ratio, only the one that feels like you.

At Lindelli, our collection spans everything from antique-cut cushion diamonds to lab-grown engagement rings, giving you the freedom to choose the cut and proportions that feel perfect.

You’re welcome to explore our Sydney Atelier, where our experts will guide you through proportions, cuts and styles in person. Or, if you prefer, you can get in touch with us online. We'd love to help you find a diamond that not only sparkles brilliantly, but feels truly yours.

FAQs

What is a good ratio for a diamond?

For round diamonds, a ratio of 1.0–1.03 is ideal. For fancy shapes, the best ratio depends on the cut,  ovals (1.3–1.5), emeralds (1.3–1.5), cushions (1.0–1.40).

What is the golden ratio of diamonds?

There isn’t one universal “golden ratio.” Instead, each shape has its own ideal cut proportions that maximise brilliance, such as the 1.0 ratio for rounds or 1.3–1.5 for ovals and emeralds.