Compare the price, not the package
Two jars of the same peanut butter sit side by side: one is 16 ounces for $4.99, the other 28 ounces for $7.49. Which is cheaper? The shelf tag may tell you, but tags are not always in the same unit, and they rarely account for a sale price or a coupon. This calculator reduces each product to its price per unit so the comparison is exact.
The formula
Unit price = price ÷ quantity.
Use the same unit for both products: ounces, pounds, fluid ounces, sheets, loads or individual items. The calculator then tells you which product is cheaper per unit, by what percentage, and how much you would save on the quantity of the second product.
Saving = (higher unit price − lower unit price) ÷ higher unit price.
Worked example
- Product A: $4.99 ÷ 16 oz = $0.312 per ounce, or $4.99 per pound.
- Product B: $7.49 ÷ 28 oz = $0.268 per ounce, or $4.28 per pound.
- Product B is 14.2 percent cheaper per ounce.
- Buying 28 ounces at A’s unit price would cost $8.73, so B saves you $1.24 on that quantity.
When does B stop being the better deal?
| Price of the 28 oz jar | Price per ounce | Saving versus A |
|---|---|---|
| $5.99 | $0.214 | 31.4% |
| $6.99 | $0.250 | 20.0% |
| $7.49 | $0.268 | 14.2% |
| $7.99 | $0.285 | 8.5% |
| $8.99 | $0.321 | A is cheaper by 2.9% |
At $8.99 the large jar costs more per ounce than the small one, a situation that is more common on store shelves than most shoppers expect.
Converting units before you compare
- 1 pound = 16 ounces, and 1 kilogram = 35.27 ounces.
- 1 quart = 32 fluid ounces, 1 gallon = 128 fluid ounces, and 1 liter = 33.8 fluid ounces.
- For paper towels and toilet paper, compare per sheet or per square foot rather than per roll, since “double” and “mega” rolls vary from brand to brand.
- For detergent, compare per load, because concentrations differ.
Weight and fluid ounces are different measures. Compare a 16 oz jar of honey sold by weight with another sold by weight, not with a bottle labeled in fluid ounces.
Tips for using unit prices well
- Factor in coupons and sales. Enter the price you will actually pay at the register.
- Think about waste. A family pack that is 15 percent cheaper per pound saves nothing if 15 percent of it ends up in the trash.
- Check store brands. They often beat the national brand’s large size even in a smaller package.
- Watch for shrinkflation. When a product’s size quietly shrinks while the price stays the same, its unit price rises. Running the numbers each time you restock catches it.
The cheapest unit price is not always the best choice, but knowing it lets you decide with the full picture in mind.