Visit your local supermarket or convenience store and you are likely faced with your favorite products in a bewildering array of sizes: a Coca-Cola could be in 200ml, 330ml, 500ml, 1250ml or even 2500ml packaging. And it’s not just grocery items, but cosmetics, shampoo and candy bars, too. Anecdotal evidence suggests consumers associate package size with quality; for example, a consumer blog reported that Reese’s peanut butter cups in the smaller miniature cups were “far superior” to the normal-sized cups, while the big cup version was of the lowest quality in their estimation.

This suggests that package size – one of the most accessible and easy-to-process product cues to which consumers are exposed – can have a significant impact on quality judgments. Yet this influence has rarely been scientifically investigated, and also, even if such a size-quality effect exists, it isn’t clear why it does. Dengfeng Yan, Jaideep Sengupta and Robert S. Wyer Jr. set out to examine the relationship between packaging size and perceived quality, as well as the explanatory role of unit price perceptions.

Potato chips, shampoo, laundry detergent, orange juice in cartons and bottles of vitamin pills in varying sizes were used in a series of studies conducted with students. The results did indeed demonstrate that a product in a smaller package was perceived to be of higher quality than the same product in a larger package. Why did this effect occur? Because the smaller package was perceived to be higher in unit price – that is, based on usual supermarket experiences, consumer believed that the smaller package cost more in terms of unit volume. Exactly the same pattern of results was obtained regardless of whether the product was a food or a non-food.

Interestingly the findings indicated that quality perceptions were not driven by differences in overall, or total, price — had this been the case, the larger package, which was believed to have a higher total price in each study, would have received better quality ratings. The researchers argue that when unit price and overall price offer competing predictions of quality, unit price is the more diagnostic of the two cues. The unit price cue incorporates information about both cost (“how much do I pay”?) and value (“what’s the bang for my buck?”). Overall price only provides information about the former, and is therefore less informative. At the same time, the studies also identified conditions under which quality judgments are more likely to be guided by overall price than unit price. When overall price is the only explicitly provided price information, and consumers are too distracted to estimate unit price, consumers only end up weighing overall price – and when that happens, the larger packaging gets rated as being better.

Marketers can use the information on package size to influence consumers' quality perceptions, while the findings also provide guidelines as to the conditions under which a smaller or a larger package may be more advisable. In a busy store, for example, a larger package might actually produce inferences of higher quality, but when consumers have the opportunity to process price and size information carefully, a smaller package is likely to be preferred. If marketers want to position their products as being of high quality, it would be desirable to decrease package size. On the other hand, using a smaller package may backfire if consumers are more concerned with “value for money” rather than quality.

A word of caution: this study focused on the quality/size relationship of packaged goods. It will not necessarily hold true for all products, such cars and houses – indeed, for items such as diamonds, the bigger the size, the higher the perceived value.