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Blue Nile vs. Costco Diamonds: Buyer’s Guide

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Blue Nile vs Costco

If you’re looking for a diamond, whether for an engagement ring or another special occasion, there are many in-store and online retailers to consider.

Blue Nile brands itself as the world’s largest online diamond retailer, while Costco’s reputation extends far beyond jewelry. 

Both offer a diverse selection of diamonds, but there are many factors to explore such as price, financing, customer service, and return policies.

Our experience is that Blue Nile is the superior choice for buying a diamond because of its wide selection, image technology on its website, GIA certifications, and overall value.

But let’s compare Blue Nile versus Costco diamonds across these areas and more, so you’ll know which is best for you.

Blue Nile Overview

Blue Nile Website

Blue Nile is an online retailer known for its engagement and wedding rings, but it also sells fine jewelry in the form of necklaces, earrings, and bracelets.

It was founded in 1999 by Mark Vadon, who bought a website that sold diamonds and revamped it into what Blue Nile is today.

The company was a pioneer in selling diamonds online, a model which has since given birth to competitors such as James Allen and Ritani

Blue Nile lists diamonds directly from the manufacturer and wholesalers. 

By cutting out the in-store experience and focusing on providing customers the lowest price, they found a niche that sets them apart from high-cost retailers that focus on a personalized buying experience and a coveted brand name.

Like most of the popular jewelry stores today, they sell only conflict-free diamonds with ethical sourcing methods.

You can learn everything you need to know about the company by reading about their history on their website here, or check out our complete review of Blue Nile.

Costco Diamonds Overview

Costco Diamonds Overview

Costco’s place in the retail industry isn’t limited to diamonds. 

The membership-only wholesaler sells a variety of goods, and many consumers aren’t even aware of their selection of engagement rings.

But Costco is known for its quality, value and low prices, so it’s worth considering whether those traits apply to its diamonds.

Diamond rings are often a high-dollar purchase, so if the same discounts Costco offers on its other items apply to its diamonds, why wouldn’t it be worth considering?

Similar to Blue Nile, Costco offers an array of jewelry that include necklaces, watches, and bracelets.

They’re available online and in-person.

Costco diamonds are also conflict-free, abiding by the Kimberley Process of evaluating its sourcing methods.

What’s the Difference Between Blue Nile and Costco?

Buying a diamond is about more than finding the one with the perfect look. 

It’s about understanding its price versus quality, the buying experience, customer service, and the ability to return it for a full refund if you decide it’s not right for you.

We’ll explore buying a diamond from Blue Nile and Costco from start to finish.

Size of Selection

If you’re starting the search for a diamond ring, you want a retailer with plenty of options. 

One of the advantages of Blue Nile’s online model is it can hold a significant amount of inventory at a lower price compared to brick-and-mortar stores.

Blue Nile Diamond Selection

In fact, Blue Nile has more than 400,000 round-cut diamonds available across all carat weights. 

In addition, it offers more than 15,000 princess cuts, close to 2,000 Asscher cuts, and more than 18,000 oval cuts.

Whether you want a one-carat diamond, one with an I1 or SI2 clarity grade, or a very good cut, Blue Nile’s selection far exceeds Costco’s for every cut. 

Costco sells rings with all these types of cuts, but often only has a few options for each.

In fact, Costco doesn’t sell loose diamonds. They only sell as finished pieces of jewelry.

Blue Nile’s options of engagement ring settings are also superior to Costco. Any of Blue Nile’s diamonds can be placed in an array of settings from solitaire and halos to vintage and three-stone settings. 

Many of these settings are available in rose or yellow gold or platinum.

Costco, on the other hand, only has four different styles of settings on its website:

  • Multi-stone
  • Solitaire
  • Halo
  • Three-stone

Costco Engagement Ring Settings - Costco

When comparing the inventory size of Blue Nile diamonds versus Costco, Blue Nile is the clear winner.


The quality of a diamond or engagement ring isn’t determined by the retailer that sells it. In fact, there are many online and in-store retailers that sell quality diamonds.

On the other hand, buying from an established brand doesn’t guarantee high quality.

Instead, you should determine the quality of a diamond through a third-party certification.

But not all grading certificates are equal. The Gemological Institute of America (GIA) and American Gem Society (AGS) have the best reputations of reliable, consistent, and rigorous grading standards. 

While this does result in a premium charge on the diamond, it gives you confidence in its carat weight, color, clarity, and cut.

All Blue Nile diamonds are graded by the GIA, so you can be assured of its reliability. 

GIA Report from Blue Nile

Other grading labs such as GCAL or the IGI are often looser with their assessments, which means a diamond with an I color grade from the GIA may earn an H from either of those labs.

Costco’s relationship with the GIA is more complicated. The company states, “All items with a 1.00 carat or larger diamond center stone will include a GIA Diamond Grading Report detailing the center diamond.”

Other diamonds are graded by GIA-trained gemologists, but this isn’t the same as a GIA certificate. 

They’ll come with a “detailed article of description” from these gemologists, but this significantly reduces its value because the grading isn’t as reliable.

We recommend you don’t rely on these gemologists but instead buy a diamond based on the GIA or AGS grading report.

Price and Value

You should try to maximize the value of a diamond relative to its price. This is a key consideration for buying a diamond or piece of jewelry, because the industry is known for its high markups.

The way you get the most value is by focusing on the quality of the diamond and not the brand. In most cases, you’re charged a premium for a high-end brand like Tacori, Tiffany’s, Jared, or Zales diamonds

Tiffany Jared and Zales Logo

When you buy a diamond from those retailers, you aren’t just paying for the stone. You’re paying for the prestige associated with those brands.

This is why buying from Costco or Blue Nile can be the right choice for shoppers focused on value. 

There isn’t the same level of prestige associated with the diamonds from these brands, so you avoid the price premium.

In comparing Costco versus Blue Nile, it’s difficult to make a one-to-one comparison because Costco doesn’t sell loose diamonds. 

The best way to compare price is to create an equivalent engagement ring from Blue Nile and place it next to Costo’s piece.

For example, Costco sells this 1.10-carat platinum engagement ring for $8,999.99.

1.10 carat engagement ring

On Blue Nile’s website, we created a similar ring with a 1.10-carat diamond and a platinum setting.

Platinum Setting Engagement Ring

It costs $8,994.

As another example, this engagement ring from Costco with a 1.30-carat diamond in a solitaire platinum setting costs $10,499.99.

This engagement ring from Blue Nile, with the same style of setting and the same quality diamond, costs $10,757.

These examples show that Blue Nile and Costco diamonds are priced at similar rates.

When both rings include diamonds graded by the GIA, you can be confident they’re also close in value.

Buying Experience

Finding the right engagement ring isn’t only about the end product. You should also evaluate retailers based on the overall buying experience. 

This is especially true if you aren’t a jewelry expert. If you don’t understand the basics of how diamonds are priced and graded, you could overpay compared to its value.

Blue Nile has perfected the online buying experience, which is what makes them one of the best places to buy diamonds online.

Even though they don’t have the personalized service of in-store retailers, they offer extensive educational information on their website about diamonds, settings, and other jewelry.

My favorite feature on their site for engagement ring shopping is the ability to “start with a setting” or “start with a diamond”, which is found in the dropdown of the main navigation.

Build Your Own Engagement Ring

You can start by exploring the more than 600 unique settings and filter by price, metal, material, or ring style. 

Whether you’re looking for platinum, rose gold, cathedral, or non-cathedral setting, Blue Nile has plenty to offer.

Or you can start by searching through thousands of diamonds in every cut. Their image technology allows you to view a high-quality, magnified image of many of their diamonds.

From there, you pair the diamond and setting together to build the perfect engagement ring.

The same process is available for other fine jewelry at Blue Nile.

The Costco buying experience is more traditional, both online and in-person.

If you’re choosing the in-store route, don’t expect the diamond expertise you’ll find at jewelry stores. There won’t be trained gemologists on site to answer your questions.

When I went to Costco to shop for my wife’s engagement ring, it was a short trip. I examined a few rings through the glass, but none jumped out at me as the right fit.

The online experience is also mundane. Instead of the ability to build your own engagement ring, you choose from engagement rings that already include both a diamond and ring shank

The images of diamonds are also a much lower quality compared to Blue Nile.

Emerald Cut Engagement Ring from Costco

There are usually a couple hundred rings available, and that selection drops significantly as you begin filtering for price, metal color, ring style, and stone shape.

On the positive side, both the in-store and online experience aren’t complex. 

If you find the engagement ring that’s right for you, there are options available for you to pick it up in store or have it shipped.

Costco doesn’t ship jewelry to its warehouses for you to view before you buy. This contrasts with other jewelry stores such as Ritani, which will ship the ring to a local store for you to visit.

If you’re considering the overall buying experience in your choice of jewelry retailer, we recommend Blue Nile. 

It’s a user-friendly, fast process from start to finish where you can build the exact engagement ring that’s right for you.

Returns and Warranty

Jewelry is often a significant purchase, which means you need confidence you’ve chosen the right piece. 

That’s why both Blue Nile and Costco offer free returns.

You can return your diamond to Costco for a full refund, but for diamonds that weigh more than one carat, you must include the IGI or GIA report. 

It will be sent to their fulfillment center for verification before they issue your refund.

The same idea is true for Blue Nile. If you aren’t satisfied with your purchase within 30 days, you can return your jewelry for a full refund. They’ll even pay shipping costs.

Petite Cathedral Engagement Ring

You can learn more about Blue Nile’s 30-day money back guarantee here.

Costco doesn’t include information about a warranty on its website. In fact, they recommend you purchase jewelry insurance. 

Unless it’s shipped with a defect or there’s a clear manufacturer error, it doesn’t appear Costco’s jewelry warranty expands past its return policy.

Blue Nile does offer a lifetime warranty on its diamonds and jewelry.

They state that if your item has a manufacturing defect, you can return it for an inspection. They’ll either repair or replace it.

It’s important to note this warranty doesn’t include “slight irregularities and variations in craftsmanship or natural characteristics”, which also includes inclusions. 

Blue Nile says it’s part of the character of the piece and shouldn’t be considered a defect.

Its warranty and 30-day return policy means Blue Nile is the winner in this category as well.

You can read all the details on their website here.


If you aren’t able to pay the full price for your diamond ring up front, you should consider financing options.

Blue Nile and Costco don’t directly offer financing on their jewelry, but they have credit card options for those who want to extend payments over a longer period of time.

Blue Nile’s credit card offers multiple financing options with periods ranging from six to 60 months. It doesn’t include an annual fee, and it comes with member-only benefits and promotions.

Costco is similar in that they also offer credit card options with various payment periods and interest rates. You should connect with a Costco representative in-store to learn the details.

So whether you’re searching for diamonds and jewelry at Blue Nile or Costco, there are financing options at both retailers.

Customer Reviews

As with any company, there are positive and negative customer reviews about Costco and Blue Nile.

Let’s start with Blue Nile’s reviews. 

They’ve earned an A+ from the Better Business Bureau. 

Blue Nile BBB Rating

This doesn’t mean they’ve never had a complaint but instead that they have a reputation of addressing customer concerns in a productive way.

Overall, they hold 3.84 out of five stars. In reading some of the complaints, they involve topics such as slow refunds, issues with ring sizes, and the item not matching the description.

But in each case, a member of the Blue Nile customer service team has addressed the complaint and reached out to the customer. 

This is indicative of strong customer service and should give you confidence in the company.

On TrustPilot, Blue Nile has 3.9 out of five stars from more than 500 reviews.

Blue Nile Reviews

There’s also positive sentiment about Costco engagement rings online. 

For example, one customer documenting their experience wrote, “Costco is awesome! They have a great policy and reputation for all their goods including jewelry. Take the guesswork out, and if you don’t love it, take it back.”

Another buyer also wrote highly of their return policy, saying, “I have a couple of their pieces [and] love them! The return policy is great. The “I” color seems brighter, maybe because the cuts are so nice they have a lot of sparkle.”

These customer reviews reiterate the importance of buying from a trusted brand and relying on a certificate from the GIA or AGS to determine its quality.

By choosing to buy a GIA or AGS diamond from either Costco or Blue Nile, you can have confidence in all parties involved in the sale.

Should You Buy a Diamond Ring from Blue Nile or Costco?

We recommend you buy a diamond ring from Blue Nile instead of Costco. 

Blue Nile has perfected the online jewelry-buying experience over more than 20 years. From the educational content to selecting a diamond or setting to their return policies and warranty, they provide an exceptional experience from start to finish.

Combine that with low prices and quality diamonds, and you can’t go wrong choosing Blue Nile as your vendor.

That doesn’t mean there aren’t diamonds and jewelry at Costco that could be the right fit for you. You should assess their inventory in person so you aren’t only relying on stock images from their website.

By exploring a variety of diamonds and rings from Blue Nile, Costco, and other vendors, you can find the one that’s right for you.

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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