The ubiquity of the intrinsic shape of a product, package, or logo makes understanding the effect of shape on consumer judgments an important theoretical and managerial question. Drawing upon the premise that people believe heavier objects are more stable, and past research on lay theories, we examine the hypothesis that consumers use shape stability to judge weight. Eight studies provide convergent evidence that more stable shapes are perceived as heavier, which leads to higher calorie and volume perceptions. However, this effect is mitigated when volume judgments are made before weight judgment (replicating the elongation effect), when participants get access to more diagnostic information (i.e., haptic input), or when the “heavier = more stable” lay belief is challenged. These results add to the literature on spatial judgments by examining the effects of shape stability on consumers’ judgments of weight, volume, and calorie content.