A recent study investigates how shoppers make sense of changes in packaging. Not surprisingly, their estimates of pack size changes are most precise if a package changes one dimension only (e.g. its length), and least precise if all dimensions (length, width, height) differ.
The study also derives a rule which provides a reasonably close estimate of size perceptions after a redesign. Consider a box of cereal measuring 10x10x10 which changes its proportions to 20x6x6. While the new box is clearly smaller (-28%), consumers on average conclude that it is bigger. Why? They arrive at a new size estimate by adding up the relative dimension changes (+ 100% – 40% – 40% = + 20%).
Source: Nailya Ordabayeva & Pierre Chandon, Predicting and Managing Consumers’ Package Size Impressions, Journal of Marketing, September 2013