How to Compare Unit Prices at the Grocery Store
The unit price on a shelf label shows what you pay per ounce, pound, or count. Here is how to read it, check it, and use it to spot shrinkflation.
The biggest number on a grocery shelf tag is the price of the package. The more useful number is usually the small one next to it: the unit price. It tells you what you pay per ounce, per pound, per quart, or per item, which is the only fair way to compare a small jar with a large one, or a name brand with a store brand in a different size.
What a unit price is
The National Institute of Standards and Technology, which publishes the model rules many states use for weights and measures, defines unit pricing as the cost per unit of measure of goods, such as the cost per milliliter or per ounce. NIST notes that a unit price label often shows the product name and size, the price, the price per unit, and other information, and that unit pricing appears on shelf labels and on many e-commerce sites.
Shoppers do use it. NIST's 2015 guide cites a Food Marketing Institute survey finding that 78% of consumers use unit pricing when it is available, and NIST's newer page cites Purdue University researchers reporting 82% in 2024.
Doing the comparison yourself
When the label is missing, hard to read, or uses a confusing unit, the math takes seconds: unit price = package price / package size.
Here is an example with three sizes of the same pasta sauce:
| Package | Price | Size | Unit price |
|---|---|---|---|
| Single jar | $4.29 | 24 oz | 17.9 cents per oz |
| Large jar | $5.49 | 32 oz | 17.2 cents per oz |
| Two-pack | $5.00 | 2 x 15 oz (30 oz) | 16.7 cents per oz |
The two-pack is the best value per ounce even though it is not the biggest single container. Bigger is often cheaper per unit, but not always, and promotions on multi-packs or smaller sizes can flip the order.
Watch the unit of measure
NIST's best-practice guide says all sizes in a product category should be unit priced in the same unit of measure, whether the product is sold prepacked, loose from bulk, or in random-weight packages. In practice, stores do not always follow that. NIST's own example: some juices on the same aisle might be priced per gallon, some per pint, some per quart, and some per fluid ounce, which makes comparison really difficult.
When units differ, convert before comparing. Two juices as an example:
- A half gallon (64 fl oz) for $3.99 is 6.2 cents per fluid ounce, or about $2.00 per quart.
- A 52 fl oz bottle for $3.79 is 7.3 cents per fluid ounce, or about $2.33 per quart.
The 52-ounce bottle is cheaper at the register but costs about 17% more per ounce.
Useful conversions: 1 quart = 32 fl oz, 1 gallon = 128 fl oz, 1 pound = 16 oz.
Using unit price to catch shrinkflation
NIST describes shrinkflation, also called downsizing, as a product sold at the same price while its net contents are reduced. Its example is ice cream: containers of 1.44 quarts in a slightly smaller package are now commonly sold, compared with the 1.5-quart size.
Do the math at the same shelf price and the 1.44-quart container holds 4% less ice cream, which works out to a unit price about 4.2% higher. You would never notice that from the package price alone. The unit price shows it immediately, which is why NIST calls unit pricing a tool for consumers to fight shrinkflation.
Why labels vary from store to store
Unit pricing in the U.S. is not federally required. According to NIST, the model Uniform Unit Pricing Regulation in NIST Handbook 130 applies only when stores voluntarily provide unit prices, and it has never included a mandatory provision. NIST reports that nineteen states and two territories have implemented unit pricing laws or regulations. So depending on where you shop, labels may be detailed, inconsistent, or missing.
NIST's guide also recommends that sale signs include the unit price, not just the regular shelf tag. If a sale sign shows only the package price, check the regular tag or do the math yourself.
A simple routine
- Look at the unit price on the shelf label, not the package price.
- Confirm every option uses the same unit. If not, convert.
- Check the sale price per unit, not the regular one.
- Ask whether you will use the larger size before it spoils. A lower unit price only saves money if nothing is thrown out.
- Note the size of products you buy often, so you notice when a package quietly shrinks.
Key takeaways
- Unit price is package price divided by package size, and it is the fair way to compare sizes and brands.
- In the example, a 2 x 15 oz two-pack beat both a 24 oz and a 32 oz jar on price per ounce.
- Convert to the same unit before comparing; a cheaper bottle can cost about 17% more per ounce.
- Unit pricing exposes shrinkflation: 1.44 quarts at the old 1.5-quart price is about a 4.2% unit price increase.
- Unit price labels are voluntary in many places, so knowing the math matters.