National health offices define drink sizes to establish guidelines for alcohol use. International variations exist in the limits and drink sizes recommended. Surveys assessing drinking levels rely on the notion of standard drink when enquiring about participants alcohol consumption and international comparisons are difficult because of the various definitions of one standard drink. Surveys are based on the assumption that respondents know and understand the concept of standard drink and are able to use it. We reviewed studies examining participants knowledge and understanding of the notion of standard drinks as well as their ability to pour standard drinks. Across studies, participants drink sizes typically contained greater volumes of alcohol than one standard drink. This suggests that levels of alcohol consumption have been underestimated in previous research. The magnitude of this over-sizing effect varied based on types of drinks, vessel sizes, drinking habits, and research methods. Indeed, the effect was the greatest for mixed drinks and spirits, followed by wine and beer. It also increased with vessel size and was affected by respondents drinking experience. Using photographs of vessels as representations of usual drinks exhibited the strongest discrepancy compared to tasks using actual vessels; and paradigms involving pouring real alcohol seemed to lead to greater effects than those using water or colored water. Lastly, evidence suggests that these misperceptions could be corrected and that such correction may reduce drink sizes. Implications of these findings are discussed and recommendations for researchers, health promotion campaigns and policy makers are made.