Is the bigger pack really the cheaper buy?

The study collected and compared the prices of 5,389 products sold at four large stores. For 1,403 of them, or 26%, the bigger size or multipack had a higher unit price than the smaller one. A unit price is the price worked out for a fixed amount, such as 100 g or 100 ml. When a bigger pack ends up costing more per unit, it is called a quantity surcharge.

The rate was not very different from similar surveys in the United States and Europe. It showed up most often with nuts and dried fruit, and least often with detergents and cleaning products.

The study found quantity surcharges were more common in two situations: when the two sizes were close, and when the sizes were hard to compare. If the difference is small, like 450 g versus 500 g, or one is labeled in grams and the other by count, it is hard to divide in your head on the spot.

Sales can flip the order too. If only the small size is on sale, it gets cheaper than usual while the big size stays at its regular price. Grab the big one assuming it is cheaper, without checking, and you simply lose out.

It is tempting to think a lower unit price always means a better deal. But if food goes bad or changes taste before you finish it, whatever is left is money thrown away. For things that spoil quickly, like milk, or that start to smell rancid when kept too long, like nuts, think first about how fast your household actually uses them.

On the other hand, for things you always use that do not go bad, like toilet paper or detergent, there is no need to buy small if the big size really has the lower unit price. In the end, what makes something cheap or expensive is not the pack size but the price tag and how fast you use it.

In Korea, large supermarkets and big-chain grocery stores must show a unit price for designated items. The standard is fixed, such as per 100 g for honey, per 100 ml for milk and per 10 g for snacks, so you only need to compare the small number in the corner of the price tag.

Where there is no such label, divide the price by the amount. A phone calculator does it in seconds. If the two products use different units, convert them to the same unit first and then compare.