Dimensional adjective interpretation is dependent on the com-parison class – the set of object representations – against whichthe object being modified by the adjective is judged. This paperexplores the factors determining the composition of the com-parison class, arguing that real world size information and pro-totypicality play crucial parts in its determination. Researchersoften implicitly assume that only the objects in immediate vi-sual context constitute the comparison class. However, Exp.1 shows that this information from the visual context is inte-grated with knowledge of real world size and category proper-ties to form the comparison class. Exp. 2 shows that prototypeinformation is utilized when making size judgments of cartoonimages, while size judgments of objects in photographs drawmore heavily on a speaker’s prior knowledge about the actualsize of the objects in the world. Exp. 3 demonstrates that theeffects observed in Exp. 1 and 2 were not caused by the adjec-tives used, but rather reflect differences between the size of theobjects depicted in the images.