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0.9 vs 1 Carat Diamond: How to Decide

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0.9 Carat vs 1 Carat Diamonds

The carat weight of a diamond is one of its defining traits. 

For some buyers, it’s the initial filter to narrow down their selection. That’s because a diamond’s actual and perceived value is closely linked to its carat weight.

If you’re searching for an engagement ring diamond, you might consider one that weighs 0.9 or 1 carats.

The main difference between a 0.9 and 1 carat diamond is a 1 carat diamond has a slightly longer diameter, often 0.2 mm wider than a 0.9 carat diamond. They generally appear identical to the naked eye because the distinction in weight and size is so minimal.

We’ll compare 0.9 versus 1 carat diamonds across their most important characteristics, including dimensions, price, popularity, and more, so you can decide which is right for you.

Size and Dimensions

The size of a diamond is generally referring to its weight, because that’s the primary way it’s measured. 

If you’re speaking with a jeweler about a group of diamonds, they won’t first describe them by the width of its table or the height from the culet to the crown.

Diamond Proportions

Instead, the jeweler will identify them by their carat weight. One carat equals 0.2 grams, so a 0.9 carat diamond weighs 0.18 grams.

This slight difference in weight does affect its overall dimensions.

To demonstrate, we’ll compare the measurements of two diamonds.

This diamond weighs 0.9 carats.

0.9 Carat Diamond

Its measurements are 6.13 – 6.21 mm x 3.80 mm.

The first number is its minimum diameter, and the second is the maximum. 

The third measurement, 3.80 mm, is its depth. A diamond’s depth is the height from the table to the culet.

Now we’ll compare it to this 1 carat diamond.

1 Carat Diamond

Its dimensions are 6.36 – 6.41 mm x 3.87 mm.

The extra 0.1 carats do result in a wider diamond with more depth, but the differences aren’t noticeable in most cases.

For instance, if a jeweler showed you a single diamond and you were told it was either 0.9 or 1 carats, it’d be difficult to give the correct answer.

On the other hand, if you placed a 0.9 and 1 carat diamond next to each other, you could likely identify the difference if you examined them closely.

Price

Carat weight is one of the most impactful qualities on a diamond’s price. It doesn’t increase linearly. 

Instead, it’s exponential, where a one carat costs more than twice as much as a 0.5 carat diamond, and the price more than doubles from 1 to 2 carats.

To provide examples, I compiled prices for more than 500 diamonds with the same traits, except they had different carat weights. Their average prices are in the chart below.

Diamond Price vs Carat Weight

To provide a price comparison for 1 carat versus 0.9 carat diamonds, I analyzed prices for 337 diamonds from online jeweler James Allen.

They had the following qualities:

  • Cut: Ideal
  • Clarity: VS1
  • Color: G
  • Fluorescence: None
  • Grading lab: GIA

The average price for the 1 carat diamonds was $8,834, with a range of $7,740 to $12,470.

For 0.9 carats, the average was $5,977. The lowest price at that carat weight was $5,170, and the highest was $7,400.

Prices of 0.9 Carat Diamonds

On average, that’s a 48 percent premium for a 1 carat diamond over one that weighs 0.9 carats.

The reason there’s such a significant price difference is because jewelers know there’s more demand for 1 carat. 

There’s a sense of prestige a full carat carries, and many buyers are willing to pay a higher price for that satisfaction.

As a comparison, I assessed average prices for 31 0.8 carat diamonds with those same grades. It came out to $4,530.

Although the difference between them and 0.9 carats is the same, the premium for 0.9 carats is only 32 percent.

These comparisons show 1 carat diamonds aren’t the best value because the slight difference in weight is met with a substantial increase in price.

Popularity in Engagement Rings

One carat diamonds are more popular for engagement rings compared to ones that weigh 0.9 carats. 

Like I mentioned above, buyers often receive a sense of satisfaction knowing it meets that threshold even if there’s a premium.

In fact, the average carat weight for an engagement ring diamond is close to 1 carat. Estimates differ, but you’ll generally see it placed between 1 and 1.09 carats.

Take this 1 carat engagement ring as an example.

1 Carat Diamond Engagement Ring

When placed in the 14K white gold solitaire setting, the diamond commands all the attention. At this size, you don’t have to worry about it appearing small or feeling compelled to add more diamonds to the piece.

For engagement ring diamonds less than one carat, it’s common to include features like a halo or pave diamonds.

This ring with a 0.9 carat diamond includes both.

0.9 Carat Diamond with Halo and Pave

The additional gems add weight to the piece without the same price increase that would result from choosing a 1 carat diamond.

But it’s important to emphasize this isn’t essential for a stunning engagement ring. In general, you’d need to add about 20 percent to a diamond’s carat weight before it’s noticeable.

So while the naked eye can distinguish between 0.8 and 1 carat, the difference between 0.9 and 1 carat doesn’t meet that criteria.

Another way to demonstrate the popularity of 1 carat diamonds over 0.9 is comparing the selection at popular jewelers.

Blue Nile has almost 500,000 round-cut diamonds in its inventory. About 9,000 of them weigh 0.9 carats, and almost 20,000 are 1 carat diamonds.

Jewelers and diamond cutters know 1 carat diamonds are far more popular, so they choose to cut rough diamonds at that weight more often.

Color

A diamond’s color grade indicates the presence of yellow or brown in its facets. The Gemological Institute of America (GIA) developed a scale from D to Z, where D means colorless and Z identifies strong color.

Each grade is placed in one of five categories:

  • Colorless (D-F)
  • Near colorless (G-J)
  • Faint (K-M)
  • Very light (N-R)
  • Light (S-Z)

GIA Color Scale

As a buyer, you shouldn’t be too concerned with the specific color grade. Instead, it’s about finding a 0.9 or 1 carat diamond that appears colorless without magnification.

In both cases, diamonds graded H or above often meet this standard.

For example, view this high-quality image of a 1 carat diamond with an H color grade.

Now compare it to this one that earned a D.

It’s difficult to distinguish their color.

The same is true for 0.9 carat diamonds because in general, higher carat weights require improved grades to appear eye-clean.

The reason we recommend near colorless diamonds, as opposed to colorless, is because of value. You’ll avoid the price increase for a colorless diamond, but it’ll look identical.

Cut

The cut of a diamond is the most important quality in terms of its brilliance. A poorly cut diamond, no matter how large or free of inclusions or color, will appear dull.

Similar to color, the GIA created a cut scale with five grades: excellent, very good, good, and poor.

GIA Cut Scale

We recommend always choosing an excellent or ideal cut whether it weighs 0.9, 1, or any other carat weight. It’s worth the higher cost to maximize light performance.

But you should also note more than the final cut grade on the report. In fact, its cut is combination of many factors, such as:

  • Polish: the smoothness of its surface
  • Symmetry: the alignment and arrangement of facets
  • Girdle thickness
  • Proportions

Even if a diamond isn’t perfect in all these areas, it can still earn the highest cut grade.

As an example, let’s walk through the GIA report for this 1 carat diamond.

Its table percentage is 60 percent, which falls outside the ideal range of 54 to 57 percent.

But its girdle is medium to slightly thick, which is in the ideal range of thin to slightly thick.

Table Percentage and Girdle Thickness of 1 Carat Diamond

It earned excellent symmetry and polish grades.

These factors come together to result in an excellent cut. You can expect exceptional light performance and shine from this diamond.

As a comparison, we’ll examine the qualities of this 0.9 carat diamond with a good cut grade.

Its girdle, which measures thick to very thick, is outside the ideal range. It earned a very good symmetry grade. Its table percentage of 62 percent is far from perfect.

We’d expect this diamond to appear dull in comparison to the excellent cut.

Clarity

Diamonds earn clarity grades that identify the extent to which inclusions, also called clarity characteristics, affect its appearance and durability.

The GIA scale ranges from flawless to I3, where each step down the scale indicates more impactful blemishes.

GIA Clarity Scale

Similar to color, the goal isn’t to choose a 1 or 0.9 carat diamond with specific clarity grade. 

Instead, you should select a diamond where the inclusions aren’t visible to the naked eye.

It’s incredibly rare for a diamond to earn a flawless grade, so most buyers end up with one that has inclusions such as:

  • Bruises
  • Etch channels
  • Cavities
  • Feathers

In most cases, you should start your search with SI1 clarity diamonds. It may have several pinpoints scattered across the table or a transparent feather on the pavilion.

But if small enough, they’re only visible at 10x magnification.

To provide a real example, here’s a 1 carat diamond that earned a VS2 clarity grade.

1 Carat Diamond with VS2 Clarity Grade

The clarity plot on its report shows crystals, clouds, needles, and naturals.

But each instance is small. They’re likely invisible when viewed in a normal setting.

If you placed it next to this 0.9 carat diamond that earned a VVS1 clarity grade, you couldn’t tell the difference. 

0.9 Carat Diamond with VVS1 Clarity Grade

But you’d pay up to 50 percent more for that improved clarity grade.

How to Decide Between a 0.9 or 1 Carat Diamond

Deciding on a 0.9 versus 1 carat diamond involves understanding how the slight difference in weight affects its price, appearance, and performance.

Even though the two appear similar, there are several factors to consider in your choice.

Here are some guidelines to help.

You should opt for a 0.9 carat diamond if:

  • You aren’t concerned about reaching the 1 carat threshold and want to save between 30 and 50 percent on its price
  • You’re interested in increasing the total carat weight of the piece with diamond accents
  • You understand that it’ll appear almost identical to a 1 carat diamond

Explore 1 carat diamonds if:

  • You want the satisfaction of a full carat
  • You’re willing to pay the premium compared to a diamond with a slightly lower carat weight
  • You’re interested in a diamond that often stands alone in a solitaire setting

Compare 0.9 and 1 carat diamonds at in-person retailers or online jewelers that offer high-resolution images and show the grading report.

You can then create the perfect diamond ring for your occasion.

Devon Tyler

Devon Tyler

Devon Tyler is the founder of TeachJewelry.com.

He earned an Applied Jewelry Professional Diploma from the Gemological Institute of America and now brings you essential information about diamonds, settings, and more.

Devon has consulted with leading jewelry brands, and his work has been cited in Diamond Nexus and other industry publications.

He's also a member of the International Gem Society.

Devon enjoys discussing jewelry with readers, so contact him with any questions at tyler.devon@teachjewelry.com.

Learn More About Devon

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