The National Institute of Standards and Technology publishes a short set of rules that sits behind the small number printed under a grocery price. The text is called the Uniform Unit Pricing Regulation, it lives in NIST Handbook 130, and the 2026 edition spells out six rules a store follows when it shows a price per ounce, per pound or per count.
One caveat comes first. It is a model regulation, so it applies where a state has adopted it. According to a NIST update published in December 2024, nine states and one territory have mandatory unit pricing laws or regulations, eight states and two territories have voluntary unit price regulations, and 33 states and three territories have none.
1. The Rules Apply When a Store Shows Unit Prices
The scope rule is the starting point. The handbook says any retail establishment providing unit price information for packaged commodities follows the regulation’s manner of presentation. Its background states that the regulation applies only when stores voluntarily provide unit pricing information.
Random-weight packages and uniform-weight packages that already state a unit price under existing rules are left out.
A shopper who cannot find a unit price on a shelf tag is therefore not necessarily looking at a missing legal requirement, since much depends on the state. For more everyday money habits, Frenzhub has a list of wallet-friendly life hacks.
2. Every Size of a Product Must Use the Same Unit
The second rule is the one that makes comparison possible. Unit prices must be uniformly and consistently expressed across all package sizes of a commodity.
The allowed units depend on how a product is measured. Weight goods use per kilogram, per 100 grams, per pound or per ounce. Liquid goods use per liter, per 100 milliliters, per gallon, per quart, per pint or per fluid ounce. Count items can use per unit, and the regulation also lists area and length units for goods sold by the square foot or the yard.
NIST gives a ketchup example. A 32-ounce bottle at $4.99 works out to $0.16 per ounce, while a 14-ounce bottle at $3.19 is $0.23 per ounce. Wikipedia’s entry on unit price describes the number as the price for a single unit of measure, usually shown on the shelf below the item beside the total price.
3. Rounding Has Its Own Rule
Rule three covers the digits. For a unit price of $1.00 or more, the retailer rounds to the nearest cent. For a unit price under $1.00, the retailer shows either a tenth of a cent or a whole cent.
The catch is that a store must pick one method and cannot use both, and it must apply the chosen method accurately and consistently. So the same item can show 33.3 cents per ounce at one store and 33 cents at another.
4. Where and How the Tag Is Displayed
The fourth rule is about the tag itself. A unit price may appear on a sign, a shelf sticker, tag or label, or on a sticker or label on the package.
NIST’s text says signs must be displayed clearly and in a non-deceptive manner in a central location, as close as practical to the items they cover. A sign covering several brands or sizes must show the product identity and brand, the package quantity if more than one size is listed, the total retail price and the price per unit.
The regulation sets no numeric font size, but NIST’s separate Unit Pricing Guide, updated in 2025, says the factors that most improve readability are a blocked layout and the largest font size possible, along with bold text, a color background, the words unit price and a good location. The guide adds that 74 percent of shoppers use unit pricing in a store when it is available, a figure it attributes to the FMI Food Industry Association’s 2023 shopper trends report.
5. Some Items Are Exempt
Rule five lists what a store does not have to unit price. Packages under 1 ounce, or 29 milliliters, are exempt, and so are items whose total retail price is 50 cents or less.
A product sold in only one brand and one size in the store is exempt too, since there is nothing to compare. Infant formula may be priced by reconstituted volume, and variety and combination packages, such as an assorted snack box, are exempt under the Uniform Packaging and Labeling Regulation.
The 50-cent line dates to 1997 revisions that raised it from 10 cents. Craftingyourhome.com has a related list of things smart shoppers never buy at a dollar store for low-priced items.
6. Different Units Still Have to Be Comparable
The sixth rule closes a loophole. If different brands or sizes of the same commodity are sold in more than one unit of measure, the retailer must unit price them consistently.
NIST’s example is soft drinks sold in 2-liter bottles and 12-fluid-ounce cans. Both must be shown in a form that lets a shopper compare them. If metric units also appear on the package, the store may show both on the tag.
For more on everyday money habits, Frenzhub has clever frugal living tips and craftingyourhome.com has money lessons many people wish their parents had taught them.
Why the Tag Matters When Packages Shrink
NIST’s update calls unit pricing a value comparison tool that is helpful with package downsizing, better known as shrinkflation. Mouse Print, the consumer site run by Edgar Dworsky, has documented fall 2026 examples such as Welch’s grape jam going from 32 ounces to 30 and Eight O’Clock Coffee dropping two ounces from its 40-ounce bag.
If the shelf price holds steady in cases like those, the price per ounce climbs. Frenzhub’s list of things that are actually getting cheaper is a useful counterpoint, and the unit price is how a shopper confirms which way a given item is moving.
The six rules do not make every shelf tag easy to read. They do set a common frame: same units across sizes, consistent rounding, a clear tag near the product, sensible exemptions and a comparison across package types. A shopper who knows that frame can read the small number as a tool, not a decoration.
This article was produced with AI assistance and edited for accuracy against the sources linked above.
Image: Wolfmann – CC BY-SA 4.0/Wikimedia Commons
