Start with Our Diamond Quiz
Why Are Diamond Proportions Important?
Diamond proportions are important because they directly affect how light interacts with the stone. Ideal diamond proportions allow light to enter the diamond and reflect back, creating that bright, white sparkle diamonds are famous for.
If proportions are too shallow, too deep, or asymmetrical, the diamond can appear dull, lack sparkle, or display uneven light patterns, significantly reducing its beauty and value.
The most valuable diamonds have ideal proportions that maximize these light properties. This is why cut quality (which includes proportions) is one of the 4 C's of diamond grading, alongside carat, color, and clarity.
What Is a Length-to-Width (L/W) Diamond Ratio?
The diamond length-to-width ratio (often shortened to L/W ratio) is a numerical value that expresses the relationship between a diamond’s length and its width. This measurement helps describe the overall shape of a fancy-cut diamond — whether it looks long and slender, short and wide, or perfectly square.
- A higher L/W ratio means the diamond appears longer and narrower.
- A lower L/W ratio indicates a more square or compact appearance.
This ratio is especially important for fancy shapes like oval, marquise, radiant, pear, and emerald cuts, where the outline can vary dramatically. Round diamonds are always close to a 1.00 ratio, so the concept is less relevant for them.
How to Calculate Diamond Ratio
The diamond ratio is calculated by dividing the length by the width of the diamond (both measured in millimeters): Length ÷ Width = Length-to-Width Ratio
For example:
- A diamond that is 10.0 mm long and 7.0 mm wide has a L/W ratio of 1.43.
- A diamond that is 6.5 mm long and 6.5 mm wide has a ratio of 1.00.
Length and width are typically listed on the diamond’s grading report. You can also ask your jeweler to provide these measurements if they aren’t listed online.
Diamond Ratio Chart
Diamond Shape | Ideal L/W Ratio |
|---|---|
Oval | 1.30–1.50 |
Pear | 1.45–1.75 |
Marquise | 1.75–2.25 |
Radiant | 1.20–1.35 |
Emerald | 1.30–1.50 |
Round | ~1.00 |
Cushion | 1.00–1.10 |
Princess | ~1.00 |
Asscher | ~1.00 |
Heart | 0.90–1.10 |
Best Ratio for Each Diamond Shape
Ideal Oval Diamond Ratio
The ideal oval diamond ratio is between 1.30 and 1.50. This range provides an elongated look that flatters the finger without appearing too narrow or stretched. A 1.30 ratio tends to be softer and more rounded, while a 1.50 ratio appears to be longer and more slender. Ratios above 1.50 may begin to look too thin and may emphasize the bow-tie effect, a shadow that runs across the center of the stone.
Ideal Pear Diamond Ratio
For pear-shaped diamonds, the recommended ratio is between 1.45 and 1.75. A ratio close to 1.50 is considered balanced, while a 1.70+ ratio creates a longer, more dramatic teardrop shape. The right proportion enhances the stone’s symmetry and ensures the point and rounded end are in harmony.
Ideal Marquise Diamond Ratio
Marquise diamonds typically have a length-to-width ratio between 1.75 and 2.25. A 2.00 ratio is widely viewed as ideal for a sleek, elongated shape that doesn’t look too narrow or stubby. This shape can maximize finger coverage and carat appearance, making it a popular choice for those seeking bold proportions.
Ideal Radiant Cut Diamond Ratio
The ideal radiant cut diamond ratio depends on whether you prefer a square or rectangular shape:
- Square radiant cuts: L/W ratio of 1.00 to 1.05
- Rectangular radiant cuts: L/W ratio of 1.20 to 1.35
A 1.25 ratio is often considered ideal for a rectangular radiant, offering a flattering elongated silhouette with brilliant faceting.
Ideal Emerald Cut Diamond Ratio
Emerald cuts typically fall within the 1.30 to 1.50 range. A 1.40 ratio is widely considered the sweet spot, providing a refined rectangular shape that emphasizes the stone’s step-cut facets and clarity. Lower ratios may appear too boxy, while higher ratios can look overly stretched.
Ideal Round Diamond Ratio
Round diamonds are perfectly symmetrical, so the ideal L/W ratio is 1.00. Any noticeable deviation from this (e.g., 1.02 or higher) could make the diamond appear out of round. A high-quality round brilliant cut will always have a ratio extremely close to 1.00.
Ideal Cushion Diamond Ratio
Cushion cut diamonds vary more than most shapes. The ideal ratio depends on your style:
- Square cushion: 1.00 to 1.05
- Elongated cushion: 1.10 to 1.20
Elongated cushions are popular for their finger-flattering shape, while square cushions have a vintage appeal and work well in halo settings.
Ideal Princess Diamond Ratio
Princess cut diamonds are meant to be square, with an ideal ratio close to 1.00. A range between 1.00 and 1.05 is acceptable. Anything above 1.05 may start to look rectangular and stray from the traditional princess silhouette.
Ideal Asscher Diamond Ratio
Like princess cuts, Asscher cut diamonds are designed to be square. The ideal L/W ratio is 1.00, with minor variations up to 1.05 still considered visually square. An Asscher with a high ratio will lose its iconic concentric-square pattern.
Ideal Heart Diamond Ratio
The ideal heart diamond ratio is between 0.90 and 1.10. A ratio of 1.00 ensures a symmetrical, well-defined heart shape with even lobes and a sharp point. A too-wide or too-narrow heart may appear distorted or unbalanced.
Diamond Proportions & Diamond Ratio FAQ
What is the best oval diamond ratio?
The best ratio for an oval diamond is typically 1.35 to 1.50. A ratio within this range gives the diamond a pleasing, elongated look without distorting the shape.
Why does diamond ratio matter?
The length-to-width ratio directly affects how the diamond looks on the finger. A higher ratio gives a slimming, elongated look, while a lower ratio appears wider and more compact. Choosing the right ratio enhances both the diamond’s appearance and how it complements your hand.
Can you change a diamond’s ratio?
No, the ratio is determined when the diamond is cut. However, you can choose a different shape or setting to influence how the diamond appears visually.
How does diamond ratio affect price?
In general, diamonds with uncommon but desirable ratios may be priced slightly higher due to demand. However, cut quality, carat, color, and clarity have a greater impact on price than L/W ratio alone.
