Understanding consumer response to product supersizing and downsizing is important for policy makers, consumer researchers, and marketers. In three laboratory experiments and two field studies, the authors find that changes in size appear smaller when packages and portions change in all three spatial dimensions¿height, width, and length¿than when they change in only one dimension. Specifically, they show that size estimations follow an inelastic power function of the actual size of the product, especially when all three spatial dimensions change simultaneously. As a result, consumers are more likely to supersize their orders when products change in one dimension and are more likely to downsize their orders when products change in three dimensions. When changing dosage, consumers pour more product into and out of conical containers (e.g., martini cocktail glasses, in which volume changes in three dimensions) than cylindrical containers (e.g., highball glasses, in which volume changes in one dimension). Finally, consumers expect (and marketers offer) steeper quantity discounts when products are supersized in three dimensions than when they are supersized in one dimension, regardless of whether size information is present.