Comparing product prices by the ounce, pound, count, or other unit of measure can help you find the best value and save money. That’s why some states require retailers to display the so-called unit price along with the item price. But in some cases, unit prices don’t allow for an accurate comparison.
For example, in the stores we checked, unit prices for paper towels were shown as price per 100 sheets. The problem with that is that the sheet size can vary by brand, with the biggest difference being between rolls with full-sized sheets and those with select-a-size sheets, which are perforated to be about 40 percent smaller. As a result, select-a-size rolls typically have more, albeit smaller, sheets, which can yield a much lower cost per 100 sheets than their full-sheet counterparts, even if the roll is more expensive, as is sometimes the case.
To find the best value, you should recalculate the unit price based on area, such as total square feet per roll, which typically is listed on the package. Your cell phone’s calculator app can help. Of course, if you and your family are likely to use just one select-a-size sheet for every full-sized sheet you would otherwise tear off the roll, select-a-size may be the better value even if it has a higher square-foot unit price. That's something you may be able to tell over time.
Use our supermarket, laundry detergent, and paper towel buying guides. And read our recent report on the move by some retailers to begin showing unit prices online.
Another example is liquid laundry detergent. We found stores showing unit prices for laundry detergent in price per fluid ounce. The issue here is that these products are sold in different concentrations. So a bottle of a company’s “2x” formulation may not wash the same number of loads as its “3x” product. Yet, the unit price makes no distinction. To do a true cost comparison, you should recalculate the unit price by dividing the total cost by the number of loads per container, which you’ll find on the label. Of course, when doing your laundry, you should follow the directions for the proper amount to use. Using too much not only wastes money, but can leave clothes with soap residue. Incidentally, designations such as “2x” and “3x” refer to different concentrations of a manufacturer’s products and are not meant to be used to compare brands.
You need to do the same thing with powder laundry detergents, which also come in various concentrates but were all priced per ounce in the stores we checked.
The big challenge is with dishwashing liquids, which come in concentrated and non-concentrated versions, both of which we found being unit-priced by the ounce. What makes this really difficult is that the bottles usually don’t include instructions on how much to use, so there’s no way to factor in the theoretical advantage of the concentrated formula.
Our best advice? Be your own consumer test expert. Compare concentrated and non-concentrated varieties, and choose the one that works for you and has the lowest unit price.
One final note. Some stores don't recalculate unit prices for items on sale, and instead display the unit price based on the full item price. So don't be tricked into comparing apples with oranges, so to speak.
—Anthony Giorgianni
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