This study shows that exposure to topic-related but irrelevant information enhances both estimates of peer knowledge and our own sense of knowledge. In Experiment 1, participants were more confident in their answers to general knowledge questions and gave higher estimates of peer knowledge when such questions were accompanied by short paragraphs containing topic-related yet nondiagnostic information than when they were not. The inflated peer knowledge estimates were independent of the classic curse of knowledge. Experiments 2, 3, 5, and 6 demonstrated that irrelevant information biases knowledge estimation via its semantic relatedness to the test questions; response latencies were measured in Experiments 5 and 6 to examine the possible role of retrieval fluency in the semantic relatedness effect. Experiment 4 attributed the bias to information content (e.g., "it is generally known that "keratin" is responsible"), not comments on knowledge popularity (e.g., "'what' is responsible is generally known"). Importantly, the effect of irrelevant information on estimates of peer knowledge was fully mediated by confidence in own knowledge in Experiments 1, 2, 4, and 5. Experiment 6 manipulated retrieval fluency and failed to find conclusive evidence for its involvement in the semantic relatedness effect. We conclude that irrelevant information boosts peer knowledge estimation through its semantic relatedness to the problem at hand, and the effect is mostly explained by a corresponding increase in the individual's own sense of knowledge.