Guide ยท Unit prices
How to compare grocery prices by unit price
What a unit price is
A unit price is the package price divided by how much is in the package. A $3.49 carton of 64 fl oz orange juice is 5.5¢ per fluid ounce, or $6.98 a gallon. A $5.99 gallon is $5.99 a gallon. The gallon is cheaper even though its price is higher.
Grocery unit prices come in three kinds, and you can only compare within one kind:
- By weight: per ounce or per pound. Meat, cheese, coffee, rice, most dry food.
- By volume: per fluid ounce, quart or gallon. Milk, juice, broth, oil.
- By count: per item or per dozen. Eggs, rolls, pods.
Pick the unit that makes the numbers readable: per pound for meat, per gallon for milk, per dozen for eggs. The shelf tag in most US stores prints a unit price already, but not always in the same unit from one store to the next.
Six label traps, all from real listings
Each of these made a price look far cheaper than it was, in a real store listing, until we taught Cartworth to read it correctly.
1. "12 ct, 15 oz" is not twelve 15 oz bags
A bag of Hawaiian rolls listed as "12 ct, 15 oz" is twelve rolls weighing 15 oz in total. Read as twelve 15 oz packs, a $2.69 bag works out to 24¢ a pound. The real figure is $2.87 a pound. In US labelling, a piece count followed by a weight almost always means pieces, with the weight being the whole package.
2. "8oz, 9ct" is nine slices, not nine packs
Sliced cheese listed as "8oz, 9ct" is nine slices in one 8 oz pack. Read as nine packs, $5.49 looks like $1.22 a pound. It is $10.98 a pound. When the name counts containers ("Yogurt Cups, 5.3 oz, 12 Count"), it really is twelve cups; when it counts pieces, it is one package.
3. Warehouse clubs state one unit's size and charge for the pack
"Kerrygold Pure Irish Butter, 8 oz, 4-count" is four 8 oz blocks, 2 lb in all. Warehouse clubs write the size of one unit and the count after it, hyphenated. Divide the price by one block and the butter looks four times dearer than it is.
4. A price per pound shown as a package price
A listing reading "Ground Chuck, 10 lb, $7.99" looks like 80¢ a pound. The small print under it said "$0.50/oz", which is $7.99 for one pound. Stores that sell meat and cheese by weight sometimes publish the per-pound price against a typical package size. If a big package looks impossibly cheap, check the per-ounce line.
5. "32 oz" of broth is a quart, and "10.5 oz" of soup is not
Drinks and broth are sold by volume, so a "32 oz" carton of broth means 32 fluid ounces, a quart. A can of condensed soup is sold by weight: 10.5 oz of food, not 10.5 fluid ounces. Comparing a weight with a volume gives a number that means nothing.
6. "Each" against "per pound"
Bananas are sold per pound in one store and at so much each in the next; avocados, peppers and melons too. You can only compare them by assuming a typical weight for one piece, which makes the result an estimate. Treat it as one.
Habits that avoid all six
- Compare unit prices, never package prices, and only in the same kind of unit.
- When a price looks far better than every other store's, read the size line and the per-unit line before you believe it.
- For multi-buy deals ("2 for $5"), check whether you have to buy two to get the price.
- Remember that an online price is a different number from the shelf price (see Instacart vs in-store prices).
How Cartworth does it
Cartworth converts every price it finds to one unit per search, reads each of the traps above, and when a listing contradicts itself (its size says one thing and its own per-ounce line another) it keeps the package price but refuses to use the listing as the best price. See how it works.