For some of your food shopping, membership warehouse clubs offer low-cost alternatives to supermarkets. We surveyed Costco and Sam’s Club. These warehouse 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, warehouse stores, which specialize in bulk sales, stocked a larger portion of our market basket items. Sam’s Club had 56 percent and Costco 32 percent.

The figure below indicates how much warehouse stores could save you. Since the warehouse stores 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 stores’ prices for amounts specified in the market basket. After this adjustment, we compared the prices of items at the warehouse stores 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 stores were usually larger than the sizes of the items priced at the other stores, so the warehouse stores enjoy an advantage in such a comparison.

We found prices at Costco were about the same as those at Sam’s Club, and that these two warehouse clubs offer significant savings. For example, prices at Costco and Sam’s Club beat those at Jewel-Osco by a whopping 28 percent. We found Costco and Sam’s Club offered significant savings compared to even the lowest-priced local grocery store options: Their prices were 11 percent lower than Woodman’s and 17 percent lower than Walmart’s.

In addition to having low prices, Costco received very high ratings from its customers for the quality of its meat and above-average scores for produce quality and overall quality. (Sam’s Club’s ratings were considerably lower than Costco’s.)

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