You don't need a Costco membership to shop its Kirkland collection - but there's a catch

Shutterstock/Arne Beruldsen

Costco's low-cost Kirkland Signature brand.

• You don't need a Costco membership to shop its Kirkland Signature collection.
• A limited selection of these items is available on Walmart and Amazon's third-party marketplace.
• In some instances, however, the items are more expensive than if you were to shop at Costco.
• Visit Business Insider's homepage for more stories.

Costco shoppers can't get enough of its Kirkland private label products. So much so, that sales from these products now account for nearly a third of its overall sales.

UBS recently estimated that the brand could be worth as much as $75 billion, which it estimates is around $15 billion more than Estee Lauder, for example.

Read more: Costco's Kirkland brand has become a secret weapon worth as much as $75 billion

For some, having access to these low-cost staples is the very reason to buy a Costco membership, but it doesn't have to be. This is because you can pick up Kirkland products on both Amazon.com and Walmart.com through its third-party marketplace. In fact, there is an entire storefront on Amazon devoted to Kirkland products ranging from toilet rolls to vitamins to basic food items.

On Costco's website, it states that Business Members are able to purchase items for resale but must inform the warehouse membership counter before doing so. There's one key catch to this loophole, however. That is that some of these items are more expensive on Amazon and Walmart's sites versus Costco's, and their assortments are also more limited.

Take toilet rolls, for example. 30 Kirkland rolls at Costco.com costs $19.99 with a $3 shipping fee. On Amazon.com, the equivalent set costs between around $30 with free shipping.

The bonus here is that you don't need to spend the money on a Costco membership to have access to these products. However, the benefit of the membership is you have guaranteed low prices once you're through the door.

It's clearly appealing to some shoppers though. Business Insider's Hayley Peterson previously reported that Amazon was the number one seller of Kirkland products, accounting for 70% of its online sales, citing data from researcher 1010data.