THE SHORT ANSWER
Compare price per unit, not the price tag alone
Products with different sizes or quantities cannot be compared fairly by their sticker prices. Divide each price by its amount to find the unit price, then compare like with like.
A larger package is not automatically the better deal
Suppose Product A is $4.99 for 14 oz and Product B is $6.49 for 20 oz. Product A costs about $0.3564 per oz, while Product B costs about $0.3245 per oz. Product B costs more at checkout, but about 8.9% less for each ounce.
This is the same idea behind shelf labels such as “price per ounce” or “price per 100 g.” The more package sizes differ, the less useful the sticker price is on its own.
The unit-price formula
Use one unit for both products before doing the math. For example, convert pounds to ounces or liters to milliliters first. You can express the result as price per ounce, per 100 g, per fluid ounce, or per item—just keep the same unit for both products.
When the lowest unit price is not the whole answer
- You may not use it all. A bulk package can cost less per unit but still be wasteful if it expires or goes unused.
- The products are not equivalent. Ingredients, quality, features, or included items can make a direct price comparison incomplete.
- A discount changes the price. Use the after-discount price if a coupon or promotion applies to only one option.
- Multipacks need the total amount. A two-pack with three items in each package contains six items in total.
Unit price tells you how much you pay for the same amount of a product. It is a useful starting point, not a rule that the largest package is always right for you.
Comparing a product to its old package
For a product you buy regularly, it can also help to compare today’s size and price with the old package. Our Shrinkflation Calculator measures the change in unit price when the package size, price, or both have changed.