The alcohol content in beer varies depending on the brand and type of beer. On average, a full pint (0.57 liter) of beer with an alcohol content of 5% contains about 8 grams of alcohol.
In order to determine how much per mille 3 beer would be, you would first need to know how much alcohol is in each beer. Since there is no specific information about the type of beer you use, I can only give an estimate based on an average beer with 5% alcohol.
If we assume that each beer is a full pint with an alcohol content of 5%, then 3 beers would contain approximately 24 grams of alcohol. To convert this to promille, you would have to divide the number of grams of alcohol by the number of liters of blood in the body. An adult man has about 5.5 liters of blood and an adult woman has about 4.5 liters of blood.
So if we assume that an adult man drinks 3 beers with 5% alcohol, his blood alcohol content would be about 0.44 promille.
It is important to note that this is an estimate and that the amount of alcohol a person can consume can vary depending on many factors such as weight, gender, age, medication use and even length of time of consumption. In addition, it is also important to note that the legal blood alcohol limit is around 0.05 BAC in many countries, and around 0.08 BAC in some countries.