Understand What a Standard Drink is
For your written DMV test you should know and understand what a standard drink is.
Basically, a standard drink is a unit of measurement. It is used to compare drinks with the same amount of pure alcohol, regardless of the container size or type of alcoholic beverage.
The term can give an indication of alcoholic content of a serving, just as nutrient information on your food items tells you how much fat, carbs, or protein there is in a serving. It is, however, important to understand that a standard drink isn’t always a normal serving size.
Compare Pure Alcohol Content
In the United States, a standard drink contains about 0.6 fl oz. or 14 grams of pure alcohol.
This corresponds roughly to:
- 12 fl oz. of regular beer.
- 5 fl oz. of table wine.
- 1.5 fl oz. shot of 80-proof distilled spirits.
In other words, it doesn’t matter if you drink a standard drink of beer, wine, or spirits. They all contain the same amount of pure alcohol and will affect you the same way. The same amount of alcohol will enter your bloodstream and most likely make you a poor driver.
But as you already know, a standard drink isn’t always a normal serving size. A 16 oz. glass of beer, as an example, is 1 1/3 standard drink. Since beers range from approximately 3.3% to more than 10% ABV, a 16 oz. glass of beer can contain up to 2 ounces of pure alcohol (more than three standard drinks).
How to Calculate Pure Alcohol Content
You can calculate the pure alcohol mass in a serving as long as you know concentration, density and volume. Pure alcohol has density of 789 g/l (at 20°C).
Pure alcohol mass = volume x (alcohol by volume x volumetric mass density).
A bottle of 0.35 l. (12 oz.) beer with ABV of 5.5% has 15.2 grams (0.53 oz.) of pure alcohol.
Killing the Myths
Some of the most common myths about alcohol may show up on your test (often as the false choices). It is a good idea to learn them.
- It isn’t true that beer gets you less drunk. The amount of alcohol in your blood depends mainly on how much (pure) alcohol you drink, during how long time, and your body fat.
- A cold shower, fresh air or hot coffee will NOT sober you up. You may feel better, but only time can reduce the amount of alcohol in your blood.
- Alcohol is NOT a stimulant. It is actually a depressant that slows you down.
Note that the standard sizes are sometimes expressed slightly different in your driver’s manual.
Standard drinks also vary in size between countries. A standard drink has less alcohol in Australia, but more alcohol in Japan.