For some food shopping, warehouse clubs offer low-cost alternatives to supermarkets. We surveyed Costco and Sam’s Club. These two stores carried few if any of the items in our market basket in the usual sizes, but when we looked for the same brands regardless of size, these two warehouse clubs—which specialize in bulk sales—stocked a larger portion of our market basket items. Sam’s Club had 51 percent and Costco 40 percent.

The figure below indicates how much warehouse clubs could save you. Since Costco and Sam’s Club stocked so few items in the sizes of our basic market basket, we looked for items of any size, so long as they were the same brands. We then used unit prices (for example, price per pound) to calculate the warehouse clubs’ prices for amounts specified in the market basket. After this adjustment, we compared the prices of items at the warehouse clubs with prices for the same brands at several other stores. Bear in mind that this is not an “apples-to-apples” comparison—the sizes of the items priced at the warehouse clubs were usually larger than the sizes of the items priced at the other stores—so the warehouse clubs enjoy an advantage in such a comparison.

Both warehouse clubs offer significant savings for most shoppers. Sam’s Club, for example, beat Target’s prices by a whopping 38 percent. And compared to Target, the savings were about 27 percent at Costco. But Costco offered only small savings compared to Walmart and WinCo, the lowest-priced local grocery store options in our survey.

In addition to having low prices, Costco received very high customer ratings for the quality of its meat and scores near the averages for produce quality and overall quality.

While Costco and Sam’s Club offered significant savings compared to prices offered at most grocery stores, these savings perhaps aren’t enough to justify paying these clubs’ annual membership fees if you don’t use them often. And if half of what you buy is wasted due to spoilage, you won’t save by buying in bulk.