Competitions are widely used by businesses and nonprofit organizations to enhance customer engagement and foster interactions among consumers. But how can consumers be effectively motivated to participate in competitions that are large (vs. small) in size? Five studies involving a variety of competitive contexts show that, holding the objective likelihood of winning and competition prize constant, consumers tend to perceive a lower likelihood of winning and a smaller prize magnitude when the competition is larger in size. These differences in perceived likelihood of winning and perceived magnitude of competition prize can jointly impact consumers’ participation in competitive situations (Studies 1a, 1b, and 2). Moreover, presenting information that enhances perceptions of winning likelihoods (Study 3) or prize magnitudes (Study 4) can remedy the negative impact of a larger competition size on participation levels. The studies also show that the underlying roles of perceived likelihood of winning and perceived prize magnitude are distinct from the role of social comparison. Overall, these findings add to consumer psychology theories and offer actionable managerial insights.