A unit price is the cost of one standard measure of a product — per ounce, per pound, per 100 sheets, per fluid ounce. It lets you compare packages that are not the same size. Many shelf tags print it in small type near the total price, and the arithmetic is simple when they don't: divide the package price by the number of units in the package.
The comparison only holds when both tags use the same unit. A tag reading "per quart" and one reading "per fluid ounce" are not comparable until you convert one of them.
A realistic example
Say a 16-ounce bag of rolled oats is priced at $3.20 and a 42-ounce container of the same style of oats is $6.30.
- 16 oz bag: $3.20 ÷ 16 = $0.20 per ounce
- 42 oz container: $6.30 ÷ 42 = $0.15 per ounce
The larger container costs less per ounce. That is only the better buy if your household will realistically finish 42 ounces of oats while they are still good, and if you have shelf space for the container. If you eat oatmeal twice a month, the cheaper unit price attaches to food that may end up discarded — in which case the effective cost per ounce eaten is higher than the tag suggests.
Unit price is a comparison tool, not an instruction. Prices, package sizes, and availability vary by store and change over time, so treat the numbers above as an illustration of the method rather than a quote.