A blood alcohol concentration (BAC) level of 0.05% means that there are 0.05 grams of alcohol in every 100ml of blood. There is no level of drinking which guarantees that a person’s BAC will stay below 0.05%. Age, body size, gender, and a range of other factors can affect the rate at which alcohol is absorbed and metabolised when you drink. Everyone is different, and two people can drink the same amount of alcohol but have different levels of alcohol in their bloodstream. However, drinking less than one standard drink per hour should keep most people’s BAC below 0.05%, as the average rate at which alcohol is metabolised is one standard drink per hour.