While I was in Australia, I noticed something interesting on a bottle of beer. In addition to listing the volume and the alcohol percentage, it also said that the bottle was equivalent to 1.2 standard drinks. I immediately asked myself, "What could that mean?"

I looked at a few other labels and saw that every bottle of alcohol contained this information. Here's what the first few bottles said:

• 330 mL, 4.5% alcohol, 1.2 standard drinks
• 375 mL, 4.4% alcohol, 1.3 standard drinks
• 500 mL, 4% alcohol, 1.6 standard drinks

I asked around, and my Australian friends said that it was a standardized way to measure how many drinks one had, since each drink has a different volume and strength. I guessed that the number of standard drinks referred to the amount of alcohol in the drink, and in the end, I was right.

A standard drink is a drink that contains 12.5 mL of alcohol. So to figure out how many standard drinks something is equivalent to, you figure out the amount of alcohol and divide by 12.5. Let's look at the examples:

• 330 mL, 4.5% alcohol: 330 * 4.5% = 14.85. Dividing this by 12.5 gives 1.188, or approximately 1.2 standard drinks.
• 375 mL, 4.4% alcohol: 375 * 4.4% = 16.5. Dividing this by 12.5 gives 1.32, or approximately 1.3 standard drinks.
• 500 mL, 4% alcohol: 500 * 4% = 20. Dividing this by 12.5 gives exactly 1.6 standard drinks. So even though this is a weaker alcohol than the others (it's a cider, whereas the others were beers), it's larger, and thus it has more alcohol.

There's a lot of information out there about standard drinks. For example, an average person's liver can break down the alcohol in one standard drink per hour. Also, it's recommended that men limit themselves to 15 standard drinks per week, and women limit themselves to 10. And there are guidelines about how many standard drinks a person can have over time and still be under the legal limit for driving. The goal of using this standard drink measure is to help people drink in moderation.

Sample Problems

1. Calculate the number of standard drinks in a 200 mL glass of wine with 12% alcohol.

2. Calculate the number of standard drinks in a 400 mL bottle of beer with 5% alcohol.

3. Calculate the number of standard drinks in a 750 mL bottle of wine with 8% alcohol.

4. Calculate the number of standard drinks in a 750 mL bottle of wine with 12.5% alcohol.

5. If someone wanted to limit themselves to 3 standard drinks, and they had a bottle of wine with 12% alcohol, how much could they drink?

6. How many 300 mL light beers with 2.8 % alcohol could someone drink if they wanted to limit themselves to three standard drinks?