Introduction: Alcohol-related harms place a significant burden on the Australian economy and health-care system. The current study aims to: (i) explore the relationship between blood alcohol concentration (BAC) and self-estimated blood alcohol concentration (EBAC); and (ii) determine whether BAC underestimation is related to an increased risk of experiencing physical aggression, verbal aggression, drink driving, ejection from a venue or refusal of service. Methods: Patron street surveys were conducted in four night-time entertainment precincts (NEP) across Queensland, Australia, between June 2016 and November 2018. Participants (N = 2144) reported on their EBAC and recent negative or harmful experiences in NEPs. BAC was measured via a breathalyser. Paired samples t tests were conducted to determine if patrons' BAC and EBAC were significantly different. Logistic regressions were conducted to examine whether BAC underestimation is a significant predictor of harm and negative outcomes. Results: Analyses identified a small, significant difference between patron's BAC and EBAC. Patrons with a low BAC were more likely to overestimate their BAC, while patrons with higher BACs were more likely to underestimate their BAC. Moderately intoxicated patrons had the most precise BAC estimations. Patrons with a high BAC and who underestimated their intoxication level were more likely to have been recently ejected from licensed venues, compared to accurate estimators or over-estimators. Discussion and Conclusions: Overall, patrons are poor evaluators of their own intoxication level, which may have implications for their experiences in NEPs. The findings highlight the need for improved BAC education for patrons.