In Australia a 'Standard Drink' is one that contains 10 grams of alcohol. Other countries have different measures which can range from 13.5 grams in Canada to 8 grams in the UK.

Regardless of variations between countries, the way the numbers roll out means that a 10g 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 how much alcohol is in the drink, multiply by 0.79 (the density of alcohol and needed to convert a volumetric percentage to grams), and then calculate how many standard drinks that represents.

Examples Of 'Standard Drink' Calculations

A 285ml glass of 4.9% (heavy) alcohol beer = 285 x 0.049 x 0.79 = 11.03g alcohol
11.03g / 10g = 1.10 standard drinks.

A 345ml bottle of 2.7% (mid strength) alcohol beer = 345 x 0.027 x 0.79 = 7.36g alcohol
7.36g / 10g = 0.74 standard drinks.

A 180ml glass of 12% alcohol wine = 180 x 0.12 x 0.79 = 17.06g alcohol
17.06g / 10g = 1.71 standard drinks.

A full nip (30ml) of 37% alcohol bourbon = 30 x 0.37 x 0.79 = 8.77g alcohol
8.77g / 10g = 0.88 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.

Examples:

1. You have been drinking for 3 hours and have had 7 stubbies of light beer in that time.

3 (hours) + 1 = 4 standard drinks "allowed" during that time
7 (stubbies) x 0.74 (standard drink equivalents) = 5.18 standard drinks
Whoops. Too many!.

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
3 (bourbons) x 0.88 (standard drink equivalents) = 2.64 standard drinks
Close! If you drink your next one slowly you should still be OK, but probably best to stop now.

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.

3. It's 8am, you really tied one on last night, but if you don't go down to the shop and get some more Coke now, you will die. You started drinking with the boys at 8pm and you must have had 15 vodkas before they poured you into the taxi at 1am. So let's do the numbers.

12 (hours) + 1 = 13 standard drinks "allowed" during that time
15 (vodkas) x 0.88 (standard drink equivalents) = 13.2 standard drinks
Guess what? You'd better ride your bike to the shop - you're probably still around 0.05.