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.