0.90 vs 1 Carat Diamond: How to Decide

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

If you’re searching for an engagement ring diamond, you might consider one that weighs 0.90 or 1 carats.

The main difference between a 0.90 and 1 carat diamond is a 1 carat diamond has a slightly longer diameter, often 0.2 mm wider than a 0.90 carat diamond. They generally appear identical to the naked eye because the distinction in weight and size is so minimal.

My recommendation is to choose a 0.90 carat diamond instead of 1 carat because they offer better value.

But let’s compare 0.90 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.

As you can see from the image below, it’s a confusing way to describe its size and doesn’t convey much to the average buyer.

Instead, the jeweler will identify them by carat weight. One carat equals 0.2 grams, so a 0.90 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 0.90 carat diamond, from the jeweler where I bought my wife’s round-cut diamond engagement ring, is viewable in high-resolution from every angle.

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.

Its dimensions are 6.36 – 6.41 mm x 3.87 mm.

The extra 0.10 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 0.90 or 1 carats, it’d be difficult to give the correct answer.

On the other hand, if you placed a 0.90 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 0.50 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.

To provide a price comparison for 1 carat versus 0.9 carat diamonds, I analyzed prices for 337 diamonds from my number one recommended 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 0.90 carats, the average was $5,977. The lowest price at that carat weight was $5,170, and the highest was $7,400.

On average, that’s a 48 percent premium for a 1 carat diamond over one that weighs 0.90 carats. Even though the 1 carat gem weighs only 11 percent more, it costs almost double the price.

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. Many buyers pay a higher price for that satisfaction.

As a comparison, I assessed average prices for 31 0.80 carat diamonds with those same grades. It came out to $4,530.

Although the difference between them and 0.90 carats is the same, the premium for 0.90 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 for Engagement Rings

One carat diamonds are more popular for engagement rings compared to ones that weigh 0.90 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.

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.

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.

For example, when I bought my wife’s engagement ring, I have to admit: It appeared smaller than what I was expecting. When I connected with the store representative, he was helpful in explaining this principle to me.

Although I was considering moving up 0.10-0.15 carats, he was willing to turn down an upsell opportunity to convey this idea. I stuck with my original purchase, and I’m glad I did.

So while the naked eye can distinguish between 0.8 and 1 carat, the difference between 0.90 and 1 carat doesn’t meet that criteria unless you’re examining them closely side-by-side.

Another way to demonstrate the popularity of 1 carat diamonds over 0.90 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 0.90 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)

As a buyer, don’t concern yourself too much with a specific color grade. Instead, it’s about finding a 0.90 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 0.90 carat diamonds because in general, higher carat weights require improved grades to appear eye-clean.

The reason I 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. That savings can be put toward improved cut or clarity grades or a setting.

Cut

A diamond’s cut is the most important quality in terms of its brilliance. A poorly cut diamond, no matter how large or free of inclusions or color, appears dull.

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

I recommend selecting an excellent cut whether it weighs 0.90, 1, or any other carat weight. It’s worth the higher cost to maximize light performance. There’s also the potential to hide inclusions or yellow shades because of scintillation.

But 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 a one 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.

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 0.90 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.

The ability to understand traits that make up a cut grade is especially important for fancy shapes such as emerald, princess, and marquise cuts.

They don’t receive traditional cut grades from the GIA like round diamonds.

To illustrate, here’s a report for a 1-carat princess cut.

So you’ll have to examine these qualities in detail.

Clarity

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

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

Similar to color, the goal isn’t to choose a 1 or 0.90 carat diamond with specific clarity grade. 

Instead, aim to select a diamond where 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, I recommend starting your search with SI1 clarity diamonds for both 0.90 and 1 carats. 

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.

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 place it next to a 0.90 carat diamond that earned a VVS1 clarity grade, you can’t distinguish between them. 

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

If you’re keeping track, this is the third way to reduce the price of your engagement ring diamond. 

Opt for 0.90 carats instead of 1 and color and clarity grades that avoid premiums but appear identical to ones with higher grades.

How to Decide Between a 0.90 or 1 Carat Diamond

Deciding on a 0.90 versus 1 carat diamond involves understanding how the slight difference in weight affects its price, appearance, and performance.

Here are some guidelines to help.

Opt for a 0.90 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 in the form of a halo or pavé
• You understand 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 and choose not to complement it with other gems

Compare 0.90 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.