How To Calculate Diamond Ratio

How To Calculate Diamond Ratio

Diamond Ratios

Many people do not realize that diamond ratios, also known as the ratio of length to width of a diamond, plays a vital role in making a diamond ring look balanced overall. Even more importantly, the ratio affects the brilliance of the diamond. Experienced diamond cutters know how to cut proportions to maximize the diamond's shine and brilliance. A diamond ring with poorly-cut proportions may look dull, or even lifeless, in comparison to other diamond rings. That is why it is crucial to talk to an experienced jeweler, and be informed before ring shopping, so that you know the ideal diamond ratios for each cut, and how to calculate it.

If you are not quite sure what you want yet, feel free to take a look at our blog post about diamond cuts to narrow down your search. Frequently, people think they want a specific cut, but in reality, they desire a specific ratio, and there are a multitude of cuts that could meet that specification. Varying ratios could make two different diamonds of the same cut look incredibly different, so it is important not to completely write off a specific cut of diamond before seeing multiple ratios.


When discussing various parts of the diamond, it is important to clarify which parts are being discussed. Length and width are measured in millimeters, looking at the diamond from an aerial view. Square diamonds have a diamond ratio pretty close to 1:1, so the particular diamond cuts listed below will typically have a higher ratio than square diamonds because they are longer. Typical diamond cuts do not have a ratio lower than 1:1. There are plenty of other measurements that go into determining the overall proportions of a diamond, but the length and width will be the ones most relevant to determining the diamond ratio.

What Is The Best Ratio Oval Cut Diamonds?

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Oval cut diamonds are one of the most popular options, but it can be difficult to pick an oval cut diamond that does not look too much like a round cut.

The ratio of an oval cut diamond is calculated by measuring the oval vertically from above, using the two ends of the diamond farthest from each other as endpoints. Then, divide that length by the width, or the horizontal length of the oval. This horizontal distance will be calculated using the two ends closest to each other as endpoints.

If the diamond ratio of an oval cut diamond is too small, then it begins to look like a round diamond, since the longest diameter and the shortest diameter start to appear about the same distance. Because of this, the ideal ratio for an oval cut diamond is pretty high compared to other cuts, around 1.3—1.5, depending on personal preference. Typically, the 1.35—1.45 range gives the classic, slender, elongated look that makes so many people love the oval cut diamond. Going lower, say, below 1.3, will make the diamond appear a little bit shorter and rounder. Going above 1.45, on the other hand, may make the diamond appear abnormally long and narrow. However, it is recommended to take a look at various ratios before deciding on your personal favorite.

The Ideal Emerald Cut Diamond Ratio

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Emerald cut diamonds are one of the oldest, tried-and-true cuts of diamonds. This classic shape is sure to please, regardless of the ratio.

Calculating the ratio of an emerald cut diamond is even simpler than for the oval cut. It simply involves dividing the vertical length of the diamond, (measured in the center of the diamond and from an aerial view), by the horizontal length, (also in the center and from above). It is important to measure in the center because the corners of the emerald cut diamond are cut off, and measuring where the corners are cut could result in a measurement that is lower than the actual length or width.

Emerald cuts also tend to be on the narrower side, and the ratio may go as high as 1.6 in extreme cases. The 1.45-1.55 range is still considered very narrow for an emerald cut diamond. People frequently opt for a diamond in the 1.3-1.45 range, which gives the diamond a more full, balanced look that appears slightly closer to a square. However, many people find the longer, slimmer emerald cut diamonds to be incredibly elegant. It is important to consider both options when looking at emerald cut diamonds. Because the emerald cut does not offer as much brilliance as other cuts, the ratio is essential for increasing shine.

Radiant Cut Diamond Ratio

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Radiant cut diamonds are incredibly similar to emerald cut diamonds, in that they both appear rectangular, with the corners cut off, from above. Radiant cut diamonds, as opposed to emerald cut ones, have more facets, or more faces on the top, where light can reflect. This makes radiant cut diamonds appear more brilliant, despite being twins with emerald cut diamonds in almost every other regard.

The ratio of radiant cut diamonds is calculated the exact same way as emerald cut ones: measuring the length and width, making sure to avoid the cut-off corners in calculations, and from above, as usual.

For a square radiant cut diamond, the ideal ratio is somewhere between 1.0 and 1.05. For a rectangular radiant cut diamond, the ratio may be anywhere between 1.05 and 1.5. However, people frequently opt for a fuller look with the radiant cut diamond. This means the "classic" radiant cut look will likely have a ratio between 1.2 and 1.35. Those looking for more of an emerald-cut inspired look may choose a higher ratio, above 1.35. Any ratio on the radiant cut is absolutely gorgeous, so there is no way to go wrong.

Contact Us

Now that you know why diamond ratios matter so much, you are well-equipped to talk to a professional about your dream diamond. Feel free to set up an appointment by emailing If you are not quite ready to schedule an appointment, please familiarize yourself with our diamonds on our diamonds page.

Diamond Ratio Calculator