How to Calculate Unit Price (and Compare It the Right Way)
Scout checked: WORKS 🟢
Unit price = price ÷ quantity. Work it out in the same unit for every pack you’re comparing (per ounce, per 100 g, per diaper, per load). The lowest number is the better deal, as long as you’ll actually use it all.
If the units match, the math is fair!
Last checked: Oct 2026 • Checked = evidence review, not a lab test
What is unit price?
Unit price is what you pay for one unit of something: one ounce, one pound, one liter, 100 grams, one diaper. NIST, the US agency that writes the best-practice guide for unit pricing, defines it as “the cost per unit of measure of goods.” (NIST SP 1181)
It’s usually on the shelf tag next to the big sticker price, often in smaller print. Many online grocery sites show it too. (Consumer Reports)
It’s how you compare a 28-ounce bag with a 32-ounce bag, or a 3-pack with a 12-pack, fairly.
The formula
Unit price = total price ÷ number of units
- Find the price you’ll actually pay. Consumer Reports says to subtract any coupons or discounts you’ll use before comparing.
- Find the quantity on the package: ounces, fluid ounces, grams, milliliters, or a count (diapers, loads, pods).
- Divide the price by the quantity.
- Do the same for every option, in the same unit.
- Compare. The lowest unit price is the best value per unit.
A real example (Consumer Reports’ numbers, not Scout’s): frozen peas at $2.48 for a 32-ounce bag work out to 7.8¢ an ounce ($2.48 ÷ 32). A 28-ounce bag at $1.99 is 7.1¢ an ounce ($1.99 ÷ 28). The smaller bag is the better price per ounce, though CR calls it “pretty much a wash.” (Consumer Reports)
Another one: a bag of 11 apples for $3.99 is about 36¢ an apple ($3.99 ÷ 11). Loose apples at 75¢ each cost more. (Consumer Reports)
Example only, made-up numbers to show the math: a pack of 20 diapers for $6.00 is $6.00 ÷ 20 = 30¢ a diaper. A box of 100 for $27.00 is $27.00 ÷ 100 = 27¢ a diaper. Here the box wins by 3¢ a diaper.
Enter the price you'll pay and the amount in the same unit for both items.
How to compare when the units don’t match
Shelf tags don’t always use the same unit, even for the same product. Consumer Reports found sugar on one store’s website priced per ounce on some packs and per pound on others. In one store, two vanilla extracts sat side by side, one priced per pint and one per quart. (Consumer Reports) NIST’s guide says stores should use the same unit across a product category, but in most of the US that guidance is voluntary. (NIST)
So convert to one unit first. The conversions Consumer Reports gives:
| US unit | Equals |
|---|---|
| 1 pound | 16 ounces |
| 1 pint | 16 fluid ounces |
| 1 quart | 2 pints |
| 1 gallon | 4 quarts |
Metric: 1 kilogram = 1,000 grams. 1 liter = 1,000 milliliters.
- Per pound → per ounce: divide the per-pound price by 16. (Example only: $3.20 a pound ÷ 16 = 20¢ an ounce.)
- Per kilogram → per 100 g: divide by 10.
- Per liter → per 100 mL: divide by 10.
- Don’t mix ounces and fluid ounces. Ounces measure weight. Fluid ounces measure volume. Compare weight with weight and volume with volume.
Traps to watch for
- The biggest box isn’t always the cheapest. The Krazy Coupon Lady found a 144-count box of Huggies Snug & Dry Size 3 at Walmart at $0.26 a diaper, while the 200-count pack listed at $0.33 a diaper. (Their example from their article. Prices change.) Check the unit price every time.
- Sheets, rolls and “mega” sizes aren’t units of measure. NIST says terms like sheets, rolls, bags, napkins and tablets should only supplement a unit price, not replace it, “as they are not units of measure.” Rolls and sheets differ in size, so compare paper towels and toilet paper by area (square feet) when the package lists it.
- Sale and loyalty prices. NIST’s guide says that when a tag shows a regular price and a sale, club or digital-coupon price, there should be a unit price for each one. If the tag only shows the regular unit price, redo the math with the price you’ll actually pay.
- Multi-buys (“2 for $5”): work out the unit price at the deal price, and only count it if you’ll buy the full deal.
- Waste costs you. “If it goes to waste, you’re paying more per unit,” Andrea Woroch, an author who focuses on shopping and budgeting, told Consumer Reports. A lower unit price only counts if you use it all before it expires.
- Shrinkflation. When a pack quietly gets smaller at the same price, the unit price goes up even though the sticker didn’t change. Comparing unit prices is how you catch it. (NIST)
Is unit pricing on every shelf tag?
Not everywhere.
- US: there’s no single national rule. Some states require unit pricing, and in many others it’s voluntary. NIST says Purdue University researchers reported in 2024 that 82% of consumers use unit pricing when it’s available. (NIST) Online, Consumer Reports found unit prices on many big grocery sites, but not all. Trader Joe’s showed none, and Walmart didn’t show it for “sponsored” listings.
- UK (Great Britain): the Price Marking Order requires shops to show a unit price where it applies. From 6 April 2026, products that can be sold by weight or volume are unit-priced per kilogram or per litre, to make comparisons more consistent. (GOV.UK guidance)
- Australia: the Unit Pricing Code is mandatory for grocery retailers selling a set range of groceries, both stores with more than 1,000 m² of grocery floor space and online grocers. Most products use per 100 g or per 100 mL. Fruit, vegetables and meat use per kilogram or per item. (ACCC; NSW Government)
Where Scout fits
That’s the whole idea behind StockUpScout: Scout shows the price per diaper, per roll, per load and per ounce, so you don’t have to do the math in the aisle. See this week’s Stock-Up List for current unit prices at our Kroger reference store.
FAQ
What is the formula for unit price? Unit price = total price ÷ quantity. For example, $1.99 for 28 ounces is $1.99 ÷ 28 = about 7.1¢ an ounce (Consumer Reports’ example).
How do you calculate unit price per kg or per 100 g? Divide the price by the weight in kilograms to get the price per kg. Divide the price per kg by 10 to get the price per 100 g. Example only: $4.50 for 750 g = $4.50 ÷ 0.75 kg = $6.00 per kg, which is 60¢ per 100 g.
How do you calculate unit price per mL? Divide the price by the milliliters. That number is usually tiny, so most shoppers use per 100 mL (× 100) or per liter (× 1,000). Example only: $3.00 for 500 mL = 0.6¢ per mL = 60¢ per 100 mL = $6.00 per liter.
Is the unit price on the shelf tag always right? Not always comparable. Consumer Reports has found tags for similar products using different units, such as pints vs. quarts and ounces vs. pounds. Convert them to one unit before you compare, and use the price you’ll actually pay.
Unit price vs. sale price: which matters? Unit price, worked out at the sale price. A sale price on a smaller pack can still cost more per unit than the regular price on a bigger one.
Is buying in bulk always cheaper? No. Check the unit price. In the Krazy Coupon Lady’s diaper example, the bigger pack cost more per diaper. And bulk only saves money if none of it goes to waste.
Sources
- NIST SP 1181-2025: “Unit Pricing Guide: A Best Practice Approach to Unit Pricing” (June 2025)
- NIST: “Uniform Unit Pricing: Tools for Consumers to Fight Shrinkflation”
- Consumer Reports: “Want the Best Grocery Deals? Use This Savings Tool” by Tobie Stanger (Oct 2, 2026)
- The Krazy Coupon Lady: “How to Get Cheap Diapers”
- GOV.UK: “Price Marking Order 2004: government guidance”
- ACCC: “Unit Pricing Code” · NSW Government: “Pricing standards”
Let Scout do the math: join the Stock-Up List
Every Thursday: the best unit prices on the essentials you always buy, and which ones to wait on. No hype.
Join the Stock-Up List
Keep reading: