In Australia a 'Standard Drink' is one that contains 10 grams (about 12.5ml) of alcohol. Other countries have different measures which can range from 13.5 grams (17ml) in Canada to 8 grams (10ml) in the UK.
Regardless of variations between countries, the way the numbers roll out means that a 10g or 12.5ml standard drink should be used for calculations in countries where a legal BAC limit of 0.05% applies.
Most beverages are labeled with their percent alcohol by volume (ie; 5%), so to calculate how many standard drinks a particular beverage serving represents you find out what percentage of alcohol is in the drink, multiply it by the serving size, and then divide it by 12.5 (ml) to calculate how many standard drinks that represents.
Examples Of 'Standard Drink' Calculations
13.68ml / 12.50ml = 1.09 standard drinks.
A 375ml bottle of 2.7% (mid strength) alcohol beer = 375 x 0.027 = 10.12ml alcohol
A 150ml glass of 11.5% alcohol wine = 180 x 0.115 = 17.25ml alcohol
A full nip (30ml) of 40% alcohol bourbon = 30 x 0.40 = 12.00ml alcohol
Standard Servings In Terms Of Standard Drinks
Alcohol Consumption In Terms Of 'Standard Drinks'
The general rule of thumb is that 2 "Standard Drinks" in the first hour will raise your BAC to 0.05%, and one "Standard Drink" per hour thereafter will maintain that level.
To do a quick calculation of whether you are over 0.05% BAC simply take the number of hours since your first drink and add 1 to it. This is the number of "Standard Drinks" that you could safely have in that period. Then calculate the number of "Standard Drinks" that you actually had, and compare the 2 results.
3 (hours) + 1 = 4 standard drinks "allowed" during that time
2. You have been drinking for 2 hours and have had 3 bourbons in that time.
2 (hours) + 1 = 3 standard drinks "allowed" during that time
BAC will vary according to gender, weight, level of fitness and age, but this quick and ready calculation can help you avoid the mistake of having "one more for the road" when you shouldn't. It's also handy next morning.
12 (hours) + 1 = 13 standard drinks "allowed" during that time