Four experiments addressed the relevance of the eigenvaluesI k of the inertia tensor for perceiving length by dynamic touch. Experiments 1–2 focused on the consequences of limiting variation in the minimum eigenvalueI 3. Both revealed that perceived length is a function ofI k . Whether the contribution ofI 3 is detected, however, depends on the range of values that characterize a particular object set. Experiments 3–4 considered the relationship between an independent index of a rod’s diameter, which does not affectI k , and actual manipulation of a rod’s diameter, which does affectI k . Whereas the former appeared as satisfaction of implicit instructions to alter reports of perceived length, the latter entailed actual differences in perceived length in accordance withI k . Results are discussed with respect to the links among actual length, perceived length, andI k , as well as, in particular, how these links guarantee that perceived length is in the range of actual lengths.