Compare two Black Friday or warehouse-club deals by price per unit – and by the price per unit you will actually use before it expires.
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With deal A price $12.99, deal A quantity 24 units, oz, rolls…, deal B price $19.99, deal B quantity 40, units you will really use 40:
Deal B is cheaper per unit you use, by 7.7%
Unit price: A $0.541 · B $0.500 · per unit used (first 40): A $0.541 · B $0.500
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Unit price = price ÷ quantity. Price per unit you use = price ÷ the smaller of quantity and units you will use before it expires. Cost of your units = packs needed (rounded up) × pack price.
Formula source: Unit price = price ÷ quantity, the unit-pricing method promoted by NIST Weights and Measures. NIST Office of Weights and Measures
Written and checked by the TanLabs Editorial Team · Last updated
Common Black Friday and warehouse-club comparisons:
| Comparison (A vs B) | A unit price | B unit price | A per unit used | B per unit used | Better buy |
|---|---|---|---|---|---|
| Paper towels: 6 rolls vs 12 rolls | $1.498 | $1.333 | $1.498 | $1.333 | B |
| Coffee: 12 oz vs 40 oz bag | $0.791 | $0.625 | $0.791 | $0.625 | B |
| Batteries: 8-pack vs 48-pack, you use 16 | $0.999 | $0.625 | $0.999 | $1.874 | A |
| Sauce: 24 oz vs 2 × 24 oz (spoils), you use 30 oz | $0.179 | $0.156 | $0.179 | $0.250 | A |
The bigger pack wins on unit price in every row, but not always on what you use: a 48-pack of batteries you need 16 of costs more per useful battery than the 8-pack.
The price for one standard unit – per ounce, per roll, per load – so packs of different sizes can be compared fairly.
Often per unit, but not always. Stores sometimes price a large pack higher per unit than a sale on the smaller one.
Many shelf tags show it in small print. Check that both tags use the same unit, such as per ounce rather than per pound.
Convert both to the same unit first, for example 1 lb = 16 oz, 1 gallon = 128 fl oz.
Rules differ by state. NIST's Office of Weights and Measures publishes model rules that many states use.
Only for things you will use before they expire and at a unit price lower than the regular sale price.
Sources: NIST Office of Weights and Measures – unit pricing and labeling