The use of standard drink units (SDUs) in the measurement of individual alcohol consumption has become widely popular in recent years. However, the ethanol content of drinks varies from country to country and is usually arrived at without scientific backing. The present study was designed to establish an SDU for a predominantly wine-drinking country (Spain). Two field studies were simultaneously conducted to gather data about home and public alcohol consumption in eight regions of the country with a total of 10751 subjects. The average alcohol content of a drink was very similar for wine and beer, whereas in the case of spirits it was almost double. Relevant differences were found across regions, drinking settings and city sizes. A Spanish SDU was set at 10 g of ethanol for wine and beer, with a measure of spirits accounting for two SDUs. The use of SDUs should be encouraged in primary health care settings. However, dispersion of data suggests that, when SDU is used as a screening tool, additional information should always be obtained in borderline cases.