“Most people know more or less what a box of cereal — or a container of ice cream or a package of coffee — should cost,” said Gourville of Harvard. “But ask them how much is in a box, and they’re relatively clueless. That’s not something they pay attention to.”

Since the 1970s, he said, conventional packages of coffee have gradually slipped from 16 ounces to about 12. Standard sizes for tins of tuna, cans of tomatoes and bottles of orange juice have all gotten smaller, too. Even the bar of Dial soap Gourville has been using for decades has become more concave, he said, in a bid to disguise its shrinking form. Henkel Corp., which manufactures Dial, did not respond to a request for comment.

Shoppers’ propensity to focus on cost over quantity, he said, also explains pricing conventions around the supermarket: Craft beer generally comes in four-packs instead of the traditional six, which would appear too pricey. At the deli counter, cured salmon is typically priced by the quarter-pound, instead of the pound measurement used for more inexpensive cuts of meats like ham or turkey.

“You might be willing to pay $9 for a quarter-pound of lox, but if the sign says ‘$36 per pound,’ you would be aghast at how expensive it is,” he said. “Companies are constantly playing around with prices.”

Often, branding experts said, companies pass off shrinking product sizes as packaging innovations. Hershey’s, for example, shaved off nearly 2 ounces from its 18-ounce packs of its dark chocolate Kisses — but kept the list price the same — as part of a 2019 makeover that swapped out its “traditional lay-down bags” for a pricier resealable, stand-up pouch

Once a brand downsizes, competitors typically follow, said Dworsky, the consumer advocate in Massachusetts who now runs consumerworld.org. Shoppers tend to compare the price of products that appear to be the same size, he said, without stopping to distinguish between a jar of peanut butter with 16 ounces and another with 15.

“As consumers, we are not completely rational: The one piece of numeric information people are sensitive to is price,” said Julio Sevilla, a marketing professor at the University of Georgia’s Terry College of Business, whose work focuses on packaging and consumer behavior. “Size matters less.”

Tillamook County Creamery Association, a farmer-owned cooperative in Oregon, reduced its family-size containers of ice cream from 56 ounces to 48 ounces earlier this year, bringing it on par with its competitors. The price, though, remained the same at about $6.

“We held onto bigger sizes for as long as we could, but at some point we decided we have to be able to make money to pass it on to the farmers who own the company, so they can stay in business,” Criteser said.

The industry standard, he added, went from 64 to 56 ounces in the early 2000s, then dropped to 48 ounces around 2008, tracking downturns in the broader economy.

But now, he said, costs are ticking up again as the industry grapples with pricier raw materials and packaging, as well as a shortage of manufacturing workers and truck drivers.

“We’ve seen costs rise before,” he said, “but we’ve never seen it happen so rapidly and all at the same time.”

Colin Booth, a political consultant in Concord, N.H., who is partial to Hefty’s tall kitchen trash bags, noticed last fall that the brand’s “mega pack” went from 90 bags to 80, while the price remained the same.

Hefty’s parent company, Reynolds Consumer Products, did not respond to requests for comment.

“I was home during the pandemic and, like a lot of people, was laser-focused on what I could and couldn’t get at the grocery store,” the 35-year-old said. “So when the box suddenly went from one round number to another, I just thought, ‘Well, will you look at that?’”