Grocery stores already give shoppers a number that is supposed to make comparing products easier: the unit price. Instead of only showing that one container costs $4.50 and another costs $7.50, the shelf label calculates how much each package costs per ounce, and most of the time the larger package looks like the better deal. But that calculation assumes every ounce will actually be eaten.
Imagine choosing between two containers of strawberries. A sixteen-ounce container costs $4.50, which comes out to about 28.1 cents per ounce, and a thirty-two-ounce container costs $7.50, or about 23.4 cents per ounce. Based on those numbers, the larger container is about 16.7% cheaper per ounce.
Now suppose eight ounces of the larger container spoil before anyone eats them. The customer still paid $7.50, but only twenty-four ounces were actually consumed, which raises the real cost to 31.25 cents for every ounce eaten. The package that looked cheaper is now more expensive than the smaller one.
The most useful question is not simply whether the larger package has a lower unit price. It is how much food can be thrown away before the original discount disappears.
In this example, the smaller container costs 28.1 cents per ounce. To match that price, someone would need to consume at least 26.7 ounces of the thirty-two-ounce container, which means the larger package stops being the better deal once a little more than 5.3 ounces are discarded, measured against the smaller package’s price per ounce. That break-even point is the most important number in the comparison, because throwing away only part of the larger package can erase the entire bulk discount.
One way to measure this after the food has been used is the consumed-unit price.
A normal unit price measures how much food someone buys, while the consumed-unit price measures how much usable food the person actually receives for the money. This is a retrospective measurement, since no one knows exactly how much food will spoil before purchasing it. Still, shoppers usually have some idea of their own habits: a family of six may easily finish a large container of strawberries, while someone living alone may repeatedly throw part of it away. The same package at the same price can therefore provide different value to different households.
Food waste is a much larger financial problem than one container of fruit. The Environmental Protection Agency estimates that more than one-third of food in the United States is never eaten, and its report estimates that wasted food costs the average American consumer $728 each year and a household of four about $2,913. Those estimates include food purchased for consumption at home and food purchased from restaurants and other food-service businesses, so they are broader than grocery-store spoilage alone.
Package size is obviously not the only reason food gets wasted. Plans change, people forget what they already have, food may be stored incorrectly, or someone may buy something with good intentions and never use it. Still, bulk discounts can make overbuying feel responsible, because the savings are visible immediately on the shelf label while the waste happens several days later, when it is easier to forget that the supposedly cheaper package was the reason there was too much food in the first place.
This is slightly different from shrinkflation, where a company reduces a package’s size without lowering its price by the same amount. Shrinkflation means receiving less than expected, while food waste means buying more than can realistically be used, but both show that the largest number printed on the shelf does not always reveal the real value of a purchase.
None of this means people should always buy the smallest package. Bulk sizes can provide real savings for larger households, for products that last a long time, or for situations where shoppers know they will finish everything. The point is that the lowest listed unit price is only a good deal when enough of the product is actually used.
Before choosing the larger package, a shopper should ask three simple questions: how much cheaper is it per ounce, how likely am I to finish it, and how much can go to waste before the discount disappears. In the strawberry example, the answer to the final question is a little more than five ounces. The best deal is not always the biggest package; it is the package that does not end up in the trash.