Unit Price Calculator
Compare the price per unit of up to three package sizes, ranked from cheapest to most expensive with the premium over the best buy.
Enter every quantity in the same unit (for example all in ounces, or all as item counts).
Updated Formula covered by automated tests
Package sizes are designed to make comparison awkward: a 12-ounce bag next to a 32-ounce bag, a six-pack next to a case of 15, a "family size" box that is only slightly larger than the regular one. The unit price calculator divides each price by its quantity so up to three options can be compared on the same footing, ranks them from cheapest to most expensive per unit, and shows how much more each of the others costs than the best one.
It is most useful in the grocery and household aisles, at warehouse clubs, and when buying online where the shelf tag with a printed unit price is missing. It works with any unit (ounces, grams, rolls, sheets, loads, pills), as long as all three items use the same one. Converting first matters: comparing a price per pound with a price per ounce, or per roll when one brand’s "double roll" has twice the sheets, gives a meaningless answer.
The formula
- price
- What you pay for the package, in dollars
- quantity
- The amount in the package in a unit shared by every item being compared
- unit price
- Dollars per one unit of quantity (shown to four decimals so small differences are visible)
- best unit price
- The lowest unit price among the items entered
Unit pricing turns a price into a rate. Because every option is reduced to the cost of one ounce, one count or one sheet, the comparison no longer depends on how the manufacturer chose to package the product. Many US states require grocery shelf tags to show a unit price, and the model regulation used by weights-and-measures officials (in NIST Handbook 130) sets which units should be used for which product categories.
The percentage figure answers the practical question of how much the convenience of a smaller package costs. A 23 percent premium per ounce means that, for the same amount of product, the smaller size costs about a quarter more.
Worked example
Sam is choosing ground coffee: a 12 oz bag for $8.99, a 32 oz bag for $19.49, or a two-pack of 10 oz bags (20 oz total) for $13.50.
- 1 12 oz bag: 8.99 ÷ 12 = $0.7492 per ounce.
- 2 32 oz bag: 19.49 ÷ 32 = $0.6091 per ounce.
- 3 Two-pack: 13.50 ÷ 20 = $0.6750 per ounce.
- 4 Compare with the best: 0.7492 ÷ 0.6091 − 1 = 23.0% more for the 12 oz bag, and 0.6750 ÷ 0.6091 − 1 = 10.8% more for the two-pack.
- 5 Buying 32 oz as 12 oz bags at the small-bag rate would cost 32 × 0.7492 = $23.97, about $4.48 more than the large bag.
Result: The 32 oz bag is the best value at about 61 cents an ounce. The two-pack is a reasonable middle option if Sam wants the coffee to stay fresh in smaller sealed bags.
Before you rely on the result
- The calculator cannot convert between units; enter every quantity in the same unit or the ranking will be wrong.
- It compares price only. Quality, concentration (for example detergent loads versus fluid ounces), waste and storage are up to you.
Frequently asked questions
Is the biggest package always the cheapest per unit?
No. Smaller sizes on sale, store brands and multipacks regularly beat the largest size, and some retailers price large packs at a premium because shoppers assume bulk is cheaper. That is exactly the assumption a unit price check is meant to test.
How do I compare toilet paper or paper towels sold as mega and double rolls?
Ignore the roll names and use the sheet count (or square feet) printed on the package as the quantity. A "mega roll" pack of 6 can contain more paper than a pack of 12 regular rolls, so per-roll prices are misleading.
Why does the shelf tag unit price differ from what I calculate?
Shelf tags may use a different unit (per pound instead of per ounce), may not reflect a temporary sale or loyalty price, and are sometimes simply out of date. Calculating from the price you will actually pay is the reliable check.
When is the cheaper unit price not the better buy?
When you will not use it all. Perishable food that spoils, products that lose strength once opened, or a size too big to store cost more per unit actually used than the label suggests.