Widely influential Duverger’s “law” and “hypothesis” describe the main direction of influence of electoral rules on party systems; however, their formulations are quite blurry what makes their application to concrete electoral results often ambiguous. Therefore, this research conducted an original survey among electoral experts (n = 131) to explore whether they apply Duverger’s rule in a consistent pattern which could lead to its less ambiguous specification. Experts’ responses revealed a considerable heterogeneity which indicates that they are often unsure about the likely outcomes of electoral systems. Nevertheless, experts were, on average, close to the central tendency predicted by the Seat Product Models [Taagepera, Rein. 2007. Predicting Party Sizes: The Logic of Simple Electoral Systems. New York: Oxford University Press] which quantifies the Duverger’s rule. Hence, experts, on average, think that election outcomes should look like what Seat Product Models predict. Therefore, the Models should be used as a baseline in electoral studies, because they allow more fine-grained evaluation of electoral systems.