Two ovals with the same carat weight can look completely different. The ratio of length to width, and how dark the middle looks, explain most of it.
Elongated diamonds such as ovals, pears and marquise cuts are popular because they look large for their weight and lengthen the look of the finger. They also vary more than rounds. Two of the things that vary most, the outline and the dark area some stones show across the middle, are not graded on a report. This guide explains how to judge both. For an overview of every shape, see diamond shapes compared.
Working out the ratio
A grading report lists a fancy-shaped diamond’s measurements as length × width × depth in millimeters. Divide the first number by the second:
- 9.10 × 6.50 mm gives a ratio of 1.40.
- 8.40 × 6.90 mm gives a ratio of about 1.22.
The grading report guide shows where to find the measurements.
Ranges many buyers look for
| Shape | Fuller look | Ranges often preferred | Slimmer look |
|---|---|---|---|
| Oval | Below 1.30 | 1.30 to 1.50 | Above 1.50 |
| Pear | Below 1.45 | 1.45 to 1.75 | Above 1.75 |
| Marquise | Below 1.75 | 1.75 to 2.25 | Above 2.25 |
| Emerald | Below 1.30 | 1.30 to 1.50 | Above 1.50 |
| Cushion | 1.00 to 1.05 (square) | Depends on taste | 1.10 and above (rectangular) |
| Radiant | 1.00 to 1.05 (square) | Depends on taste | 1.20 and above (rectangular) |
These ranges reflect popular taste, not grading standards. A chubby oval and a slim one are both legitimate choices. What matters is that you see the outline you expect before you buy, because photos taken at an angle can disguise it.
How the ratio changes the ring
A slim stone covers more of the finger’s length and makes the hand look longer, but it can look narrow on a wide finger. A fuller stone looks bolder from the side and closer to a round from a distance. The ratio also affects the setting: long stones need prongs that protect any points, as covered in prong settings explained, and a halo around a long stone becomes very long itself.
What the bow-tie is
Many elongated brilliants show a darker band across the center, roughly in the shape of a bow-tie. It appears because some facets in the middle of the stone reflect light away from the viewer, or reflect the dark shape of the viewer’s own head, instead of returning bright light. Almost every oval, pear and marquise has some bow-tie. Cutters reduce it by adjusting the angles and facet arrangement, but they cannot always remove it without losing weight.
Judging a bow-tie
| Bow-tie | What you see | Usually acceptable? |
|---|---|---|
| Faint | A slight shadow that flickers as the stone moves | Yes |
| Moderate | A visible gray band that comes and goes | Often, depending on taste |
| Strong | A solid black band from most angles | Usually not |
The test is movement. Ask for a video that rocks and tilts the stone. A bow-tie that flashes in and out adds contrast and can look attractive; one that stays dark from every angle is a problem. Static photos taken under strong lights can hide or exaggerate it.
Good to know: Look at the stone from a normal viewing distance, not only magnified. A bow-tie that looks dramatic in a close-up video can be much less noticeable at arm’s length.
Step cuts don’t bow-tie in the same way
Emerald and Asscher cuts reflect light differently, with broad flashes rather than sparkle, so they do not show the classic bow-tie. Their ratio still matters, and their large facets bring other considerations, covered in our guide to step-cut diamonds.
Pulling it together
Use the ratio to narrow down the outline you like, then use videos to judge the bow-tie. If a halo is part of the plan, check how the ratio changes the halo’s shape too; the halo guide has examples. Between two stones with similar grades, the one that looks lively and evenly bright in motion is almost always the better choice.
Quick notes
- Divide the length by the width from the grading report’s measurements to get the ratio.
- Higher ratios look slimmer and longer; lower ratios look fuller and rounder. Preferred ranges are a matter of taste, not quality.
- Most ovals, pears and marquise cuts show some bow-tie; what matters is how strong and how constant it is as the stone moves.
- Neither the ratio’s appeal nor the bow-tie is graded on a report, so photos and videos are essential.
Common questions
Q: Is a bow-tie a defect?
A: Not in itself. Some bow-tie is normal in elongated brilliant cuts. A faint one that flickers as the stone moves is usually fine; a large, solid dark band that stays visible from most angles makes the stone look dull.
Q: Which ratio makes a diamond look biggest?
A: Longer ratios cover more length on the finger and can look larger, but very long, thin stones can also look narrow. The best ratio is the one that suits the wearer’s hand and taste.
Q: Does the ratio affect price?
A: Popular ratios can be in higher demand, but grades, weight and cut quality affect price far more. Two stones with the same grades and different ratios are usually priced similarly.
Q: Do round diamonds have a ratio?
A: Yes, though it is close to 1.00. A round with a noticeably higher ratio is slightly out of round, which the report shows through the minimum and maximum diameters.