Diamond Education

What Makes the Perfect Oval Diamond (And How to Spot a Bad One)

Why Oval Is Having a Moment

Oval diamonds have been the fastest-growing shape in the market for the past five years. There are real reasons for that. An oval gives you the light performance of a round brilliant (same type of faceting) but with an elongated silhouette that looks larger on the finger and flatters virtually every hand type.

A well-cut 1.5-carat oval can visually match a 1.8-carat round. That's significant, especially if you're being smart about your budget with a lab grown stone.

But here's the catch: not all ovals are created equal. Unlike round diamonds, where GIA assigns a cut grade (Excellent, Very Good, etc.), oval diamonds get no cut grade on their certificate. You're on your own. The lab will tell you the measurements, the color, the clarity, and the fluorescence. But whether the stone is beautifully proportioned or a lifeless, bow-tie-riddled mess? That's for you to figure out.

This guide gives you the tools to figure it out.

Length-to-Width Ratio: The Number That Matters Most

The length-to-width ratio (L/W) defines how elongated or chubby your oval looks. You calculate it by dividing the length by the width.

Here's the range:

1.25-1.30: Nearly round. Some people love this chunky look, but it loses the elongating benefit that makes ovals special.
1.35-1.45: The sweet spot. This is where most people land. The diamond is clearly oval, proportional, and flattering on the finger.
1.50-1.55: Noticeably elongated. Beautiful, but preferences vary. Some love it. Others feel it looks too stretched.
1.60+: Very elongated. Starts to approach marquise territory. Can look dramatic but may show the bow-tie effect more prominently.

Our recommendation? Start at 1.35-1.50 and narrow from there based on what catches your eye. Most people gravitate toward 1.40 once they compare a few stones side by side.

The ratio should be listed on any grading certificate, or you can calculate it from the dimensions. A stone measuring 9.5mm x 6.8mm has a ratio of 1.40. Simple division.

The Bow-Tie Effect: The Make-or-Break Factor

Almost every oval diamond has some degree of bow-tie effect. This is a dark shadow that runs across the center of the stone, shaped like (you guessed it) a bow tie. It's caused by light leaking out the bottom of the diamond instead of reflecting back to your eye.

A minimal bow tie is totally normal and doesn't detract from the diamond's beauty. You might not even notice it in daily wear. A severe bow tie creates a dead zone across the widest part of the stone, making it look like someone drew a dark line through the middle of your diamond.

Here's the frustrating part: the bow tie doesn't show up on a grading report. You cannot evaluate it from a certificate. You have to look at the actual stone.

This is why buying an oval diamond purely based on specs is risky. At Ultimate Diamond, we photograph and inspect every oval we sell specifically because the bow tie is something you need to see, not read about.

When evaluating bow tie:

Acceptable: A faint shadow visible when you're specifically looking for it. When you move the diamond under light, it mostly disappears.
Moderate: Noticeable but doesn't dominate the stone. Many beautiful ovals fall here.
Severe: A dark, distracting band across the center that's visible at arm's length. Avoid these regardless of how good the other specs look.

If you're shopping online, look for HD video of the diamond, not just photos. A static photo taken under ideal lighting can hide even a significant bow tie. Video shows how light moves through the stone, and the bow tie becomes apparent.

Face-Up Size: Why Oval Wins the Value Game

Diamond carat weight is a measurement of mass, not size. Two 1-carat diamonds can have measurably different face-up appearances depending on how they're cut.

Oval diamonds, because of their elongated shape, spread their weight across a larger surface area when viewed from above. A well-cut 1-carat oval typically measures about 7.7mm x 5.5mm. A 1-carat round measures about 6.5mm in diameter.

That's a meaningful difference in visible size. Your eye perceives the oval as bigger because it covers more finger area.

This is where lab grown ovals become extremely compelling. You're already saving 70-80% compared to natural diamonds. Combine that with the oval's superior face-up size, and you're getting a stone that looks dramatically larger than what your budget would buy in a natural round.

A 2-carat lab grown oval from Le Fling can visually compete with a 2.5-carat round, at a fraction of the price. That's geometry, plain and simple.

Cut Quality: What to Check When There's No Cut Grade

Since GIA and most other labs don't provide an oval cut grade, you need to evaluate proportions yourself. Here's what to look at on the grading report:

Depth percentage: The total depth divided by the width. For ovals, aim for 56-62%. Below 56% and the stone is too shallow (light leaks out the bottom). Above 64% and it's too deep (carat weight hides in depth you can't see).

Table percentage: The width of the top flat facet divided by the total width. Target 54-60%. A table too large reduces fire. Too small reduces brightness.

Symmetry: GIA does grade symmetry for ovals. Look for Excellent or Very Good. Poor symmetry in an oval means the two halves don't mirror each other cleanly, and it's noticeable in an elongated shape.

Polish: Excellent or Very Good. This affects surface light performance.

Girdle thickness: Aim for Medium to Slightly Thick. A very thin girdle on an oval, especially at the pointed ends, increases the risk of chipping.

Color and Clarity: Where to Save

Oval diamonds show color slightly more than rounds because the elongated shape concentrates body color at the tips. If you want a colorless appearance, stick with D-F for platinum/white gold settings or G-H for yellow/rose gold (where the warm metal tone masks warmer diamond color).

For clarity, the oval's brilliant faceting does a decent job hiding inclusions. VS2 is the safe sweet spot. Many SI1 ovals are eye-clean, but you need to check the inclusion plot. Avoid SI1 stones with inclusions near the center of the table, where the bow-tie area already draws the eye.

The Shoulder Check

This is a detail most guides skip. Look at the "shoulders" of the oval, the curved sections connecting the top and bottom halves. They should be smooth, symmetrical arcs.

Flat shoulders make the oval look angular, almost like a rectangle with rounded ends. High, bulging shoulders make it look chubby. Neither is ideal.

The best ovals have a graceful, continuous curve from end to end. When you compare a few side by side, your eye will immediately identify which ones have attractive shoulders and which ones look "off" even if you can't articulate why.

The One-Minute Evaluation

If you need a quick checklist for evaluating an oval diamond:

L/W ratio between 1.35-1.50? Check the dimensions on the report.
Depth between 56-62%? On the report.
Table between 54-60%? On the report.
Bow tie acceptable? Watch a video of the stone.
Shoulders smooth and symmetrical? Look at photos or video.
Eye-clean? Check the inclusion plot, then verify visually.

If a stone passes all six, you're looking at a well-chosen oval.

What is the best length-to-width ratio for an oval diamond?

Most people find the 1.35-1.50 range most attractive, with 1.40 being the most popular single ratio. Below 1.30 looks too round; above 1.55 can look overly elongated. Personal preference matters here, so compare a few ratios before committing. Even a 0.05 difference is noticeable when you see the stones side by side.

Can you avoid the bow-tie effect in an oval diamond?

You can't eliminate it entirely, as nearly all oval diamonds show some bow tie. But you can minimize it by choosing well-cut stones with balanced proportions. The bow tie isn't listed on grading reports, so you must evaluate it visually through HD video or in person. A faint bow tie is perfectly normal and doesn't affect beauty. A severe one is a dealbreaker.

Why doesn't GIA give oval diamonds a cut grade?

GIA only assigns formal cut grades to round brilliant diamonds because that shape has standardized ideal proportions backed by decades of optical research. Oval and other fancy shapes have more subjective "ideal" proportions, and the industry hasn't reached consensus on a grading standard. This means buyers need to evaluate oval cut quality themselves using depth, table, symmetry, and visual inspection.

Are oval diamonds more expensive than round?

Oval diamonds are typically 20-30% less expensive per carat than comparable round brilliants. They also appear larger face-up for the same weight, so you're getting more visual impact for less money. With lab grown ovals, the combination of the shape discount and the lab grown price advantage makes this one of the best values in the diamond market.