How it works
The calculator converts every item to the same unit (grams for weight, milliliters for volume, or a count of items) and divides the price by the amount. The lowest price per unit is the best value.
Unit price = price ÷ size in a common unit
Worked example
Three bags of the same coffee: 12 oz for $8.99, 2 lb (32 oz) for $21.99, and 24 oz for $14.49.
Per ounce that's $0.749, $0.687 and $0.604. The medium bag wins: the small bag costs 24% more per ounce. Bigger isn't always cheaper.
Things to know
- Shelf tags already show unit prices in many stores, but not always in the same unit. One label says per ounce, the next per pound.
- Only compare like with like. Weight against weight, volume against volume. Liquids sold by fluid ounce can't be compared with solids sold by weight.
- Waste counts. A bulk pack is only cheaper if you use it before it spoils.
- Sales change the answer. A smaller pack on promotion often beats the bulk size.
Unit conversion cheat sheet
For comparing shelf tags that use different units. U.S. measures; a fluid ounce is volume, an ounce is weight.
| Size | Equals | Price-per-unit shortcut |
|---|---|---|
| 1 pound (lb) | 16 oz · 453.6 g | Price per lb ÷ 16 = price per oz |
| 1 ounce (oz) | 28.35 g | Price per oz ÷ 28.35 = price per g |
| 1 kilogram (kg) | 35.27 oz · 2.205 lb | Price per kg ÷ 2.205 = price per lb |
| 1 gallon | 128 fl oz · 3.785 liters | Price per gallon ÷ 128 = price per fl oz |
| 1 liter | 33.81 fl oz | Price per liter ÷ 33.81 = price per fl oz |
| 1 fluid ounce (fl oz) | 29.57 ml | Measures volume, not weight |
Questions people ask
How many ounces are in a pound?
16 ounces. A pound is 453.6 grams and an ounce is 28.35 grams.
Is a fluid ounce the same as an ounce?
No. A fluid ounce measures volume (29.57 ml in the U.S.); an ounce measures weight. They only match for water and liquids of similar density.
Sources
- NIST Handbook 130 (current edition): Uniform Unit Pricing Regulation
- NIST Special Publication 1181: Unit Pricing Guide
- NIST: unit conversion factors (SI units, U.S. customary)
Reviewed September 24, 2026 by The Dollars World team. How we build and check our calculators · Our data and formulas. This is general information, not financial advice.