Abstract In a usage-based framework, variation is part and parcel of our linguistic experiences, and therefore also of our mental representations of language. In this article, we bring attention to variation as a source of information. Instead of discarding variation as mere noise, we examine what it can reveal about the representation and use of linguistic knowledge. By means of metalinguistic judgment data, we demonstrate how to quantify and interpret four types of variation: variation across items, participants, time, and methods. The data concern familiarity ratings assigned by 91 native speakers of Dutch to 79 Dutch prepositional phrases such as in de tuin ‘in the garden’ and rond de ingang ‘around the entrance’. Participants performed the judgment task twice within a period of one to two weeks, using either a 7-point Likert scale or a Magnitude Estimation scale. We explicate the principles according to which the different types of variation can be considered information about mental representation, and we show how they can be used to test hypotheses regarding linguistic representations.