What is ABV (Alcohol by Volume) and how is it determined?

What is ABV?

I might be a little weird, but I like to read beer labels.  It’s amazing how much information can be found on the side of a bottle of beer.  I love to read how brewers like to describe their beer.  Some like to be serious, some like to be humorous, and some read like your drinking a fine wine created for snooty-upper-crust yuppies.  On top of having a description of the beer and sometimes the history of the brewery, there is almost always a the beer’s ABV.

ABV stand for Alcohol by Volume.  The idea is pretty straight forward.  It is the percentage of the liquid in the bottle that is alcohol.  The higher the ABV percentage, the more alcohol there is in the beer (and the more careful you’ll have to be drinking it).  But how is the ABV determined?  In case you didn’t know, the alcohol in a beer isn’t added after the fact.  So you can’t simply say, “Well we added 2 ounces of alcohol to the 16 ounce beer…so that gives this beer a 12.5% ABV.”

How is the ABV of a beer determined?

Alcohol in beer is produced when yeast converts sugar into alcohol during the brewing process.  Alcohol is actually the waste produced from yeast eating sugar….so you’re actually drinking yeast pee when you drink beer.  :)

So how do they determine how much of the sugar in a beer was turned into alcohol?  Brewers use what is called a hydrometer and some fancy math to come up with the ABV.  A hydrometer determines what the density of a liquid is compared to water.  A brewer measures the wort (beer prior to fermentation) to determine the Original Gravity (OG).  Once the yeast has done its magic, the brewer takes another measurement to determine the Final Gravity (FG) of the beer.  With these two measurements in hand, the brewer then does a little math to determine the ABV.  They subtract the Final Gravity from the Original Gravity and then multiply that number by 131.

ABV = (OG – FG) X 131

This leaves you with the percentage of alcohol that is in beer and your ABV.  For those of you who want to get a lot more information on this very interesting subject, you can check out these articles:

BeerAdvocate.com – Get to Know Your Alcohol (by Volume)

Wikipedia – Beer Measurement and Alcohol by Volume

  • http://fromthepew.blogspot.com Steve Scott


    As you may know, ABV (proof in liquor) is different from alcohol by weight, and can be a bit deceptive.

    • Anonymous

      Yeah I actually came across that studying up on ABV. It was the first time I had ever come across Alcohol by weight though. So I didn’t feel the need the mention it. Maybe I’ll need to to Beer 201 at some point. :)

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