In the autumn of 2011, a coworker in Reston, Virginia, took me to Costco for the first time. She needed mustard, by her own account. We left with a gallon of it—not a jar, a gallon, in a plastic jug with a handle, the kind of container I associated with antifreeze or pool chemicals. She was pleased. The price per ounce was a fraction of what the grocery store charged for a small squeeze bottle. By the arithmetic on the shelf tag, she had won.
I did not ask the question that later became obvious: where does a gallon of mustard live while a household of two works its way through it, and what is that space worth?
The cart should have told me something. It was not sized for a body buying groceries for a week. It was sized for a supply chain’s terminal node—forty rolls of toilet paper stacked to the child seat, a rotisserie chicken sliding around on top like an afterthought, the mustard wedged against a flat of water bottles underneath. The person pushing it was not merely shopping. She was performing the last mile of a logistics operation and calling it an errand.
Unit pricing is designed to compare packages by a common measure, and it is useful for exactly that purpose. It can tell you which mustard costs less per ounce. It does not tell you how long you will own the remaining ounces, where you will put them, or whether you will remember they are there. ([nvlpubs.nist.gov](https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.1181e2025.pdf?utm_source=openai))
This is the part the shelf tag does not compute. Formal inventory systems recognize holding costs: storage space, obsolescence, money tied up in stock, and losses through deterioration, damage, or disappearance. ([gao.gov](https://www.gao.gov/assets/ffmsr-7.pdf?utm_source=openai)) Costco, for its part, describes a business model built around low prices, high sales volumes, rapid inventory turnover, volume purchasing, efficient distribution, and reduced handling. ([sec.gov](https://www.sec.gov/Archives/edgar/data/909832/000090983225000101/cost-20250831.htm?utm_source=openai)) The warehouse club does not uniquely create the costs of household inventory, but its large packages can move more of the physical work of holding goods across the retail boundary. From then on, the customer supplies the square footage, the organization, and the patience.
For a household that consumes the product quickly and already has unused space, the arithmetic may work exactly as advertised. For my coworker, the mustard sat in a cabinet for the better part of two years. The value of the bargain therefore depended on a variable the shelf tag never mentioned: how fast this particular household could use this particular quantity—or, more plainly, how many people were eating dinner.
I have watched a more extreme version in the garage of a family of four in the same part of Northern Virginia. I have stood in this garage. A car had not been parked inside for six years because the garage had become a satellite warehouse: cases of canned goods, a chest freezer with a smaller chest freezer’s worth of organization inside it, meat bagged by type, thirty-count boxes of granola bars, and a shelving unit bought at Home Depot for the specific purpose of holding things bought at Costco. The car sat in the driveway, exposed to the weather. Nobody in that household described the granola bars and the displaced car as parts of the same transaction. The granola bars were a bargain. The car was a separate issue.
The failure of accounting is not stupidity. We price things well when they arrive as a line on a receipt and badly when they arrive as an absence: a garage that used to hold a car and now holds paper goods, a pantry so full that another jar of cumin is bought because the first one cannot be seen, ten minutes spent looking for something known to be somewhere. There is no monthly household report assigning a dollar value to the square footage occupied by toilet paper, or to the attention required to remember, rotate, locate, and eventually use it.
The overlooked feature of the bargain is not the unit price but the household balance sheet. A business accounts for inventory because storage is visibly a cost. A household rarely charges itself rent. The room already exists; the shelf has already been installed; the garage appears to be free. The expense is absorbed as clutter, inconvenience, displaced use, duplication, or waste rather than recorded as money.
Not every household has a garage to absorb it. For an apartment dweller, a renter, or someone who has downsized, surplus goods may simply become congestion. If they spill into paid storage, the carrying cost stops being invisible. It becomes a monthly bill, an automatic payment, a padlock, and a due date. The economic burden is not necessarily new. It has merely changed from domestic space that nobody invoices to space that somebody does.
The gallon of mustard was cheap. That part was true. The shelf tag was not lying; it was answering a smaller question.