This paper concerns an investigation of the manner in which typicality constrains graded membership in antonymous dimensional adjectives such as "short/tall" and "cheap/expensive" using the conceptual spaces framework. In this framework, items are organized in a space comprised of one or more dimensions along which they can be compared. The items' graded membership is established by their relative proximity in this space to the prototypical instances of contrasting concepts. Because dimensional adjectives can be applied to an indefinite variety of things and grammatically have no upper bound to serve as cognitive reference point, they have been argued to lack prototypes. We present the results of an empirical study showing that the conceptual spaces framework can nevertheless be extended successfully to dimensional adjectives by complementing them with a comparison class argument (such as "short/tall" for an adult man and "cheap/expensive" for a smartphone), allowing participants to retrieve meaningful prototypical instances, which can be used to establish membership degree. Since dimensional adjectives are subjective, we investigate how the framework can accommodate interindividual variability in membership degree judgments. We find that the predictions of the framework significantly improve if prototypical instances themselves are assumed to come with a gradient instead of being considered equally typical, thereby providing a more fine-grained account of typicality and furthering the development of the conceptual spaces framework.