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“But I only had 2 glasses of wine…”

On Behalf of | Nov 25, 2013 | Marijuana

A primer on the “Standard Drink”

In DUI defense, it is helpful for a lawyer to have a good grasp on what the client/driver consumed, when he/she consumed it, and the client’s real weight.

In the days before microbrews, calculation of a beer was fairly straightforward, because it was usually a 12 ounce bottle or can. Washington’s Liquor Control Board gave that a rating of one standard drink. Now, with beers coming in lots of different sizes, and alcohol content, that calculation has to be much more nuanced. This is particularly true because alcoholic content of beer may be by weight, rather than volume.

Here is a discussion of that topic, from The Beer Advocate website:


Alcohol By Volume

Alcohol by volume (ABV) simply represents what portion of the total volume of liquid is alcohol. Our liquid of choice is, of course, beer. And to determine the ABV of a beer, a brewer typically uses what’s called a hydrometer, which is an instrument that aids in measuring the density of liquid in relation to water (it essentially free-floats in a cylinder or liquid). The hydrometer will be calibrated to read 1.000 in water (at 60°F), and the denser the liquid (example: add sugar to the liquid), the higher the hydrometer reading.

Alcohol By Weight

Although alcohol by volume is becoming more of a standard in the U.S., don’t be fooled. Often brewers throughout the U.S. and a few parts of the world will still use what’s called alcohol by weight (ABW). If you purchase a beer that has ABW listed instead of ABV, the alcohol content is going to actually be higher than you might think. To convert ABW to ABV, simply multiply the ABW by 1.25. So a 7 percent ABW beer would be a 9 percent ABV beer. If for some reason you want to convert from ABV to ABW, multiply the ABV percent by 0.80.

A wine calculation also calls for a little more nuance. In many restaurants, if a client is buying wine by the glass, the first question is: what kind of glass, and how full was it?

You may be able to get this information from the restaurant, or you can have the client approximate with a measuring cup at home. Many people will be surprised to learn that the “standard drink”, equivalent to 1 ounce of 80 proof hard liquor, is only 3 ounces of wine, which is less than one half cup! The large red wine glasses in restaurants can easily hold three times this much without even coming close to the rim. So a client who has had “only” two glasses of wine with dinner may have had, in reality, 6 “standard drinks”. For a 150 pound person, that represents a potential BAC of .13, a significant amount over the legal limit.

Here is a link to a useful website on this subject.


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