25,000 sq. ft.

Ideal size of a 40,000-square-foot store, according to the eye-opening interview with retail expert Paco Underhill in "How Consumers Shop Differently Today," on Time.com.

Even though many American shoppers have slammed their wallets shut, retailers still need to keep shelves full so their stores don't look like liquidation outlets. But it's costly to keep megasheds stocked and still turn a profit in this economy. "I believe we have reached the apogee of the big box. Growing the store any bigger does not translate into the customer spending any more time or money," said Underhill, who also noted that "Stores on steroids will start making some choices."

Essential information: Find out whether Costco or Sam's Club offers the best value.