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Ask A Toxicologist > How does a blood alcohol concentration (BAC) relate to how much I have had to drink? Can I predict what my BAC will be based on how much I have consumed?

How does a blood alcohol concentration (BAC) relate to how much I have had to drink? Can I predict what my BAC will be based on how much I have consumed?

posted on 7:12 PM, January 6, 2014

Your BAC relates to the amount of alcohol you have consumed, your weight, and your sex. Your BAC is a measurement - this number does not mean the same thing in every person.  Intoxication and impairment are influenced by tolerance. Your tolerance relates to how you act, appear, react and think at a specific concentration of alcohol. The law defines impairment by a specific number, but impairment starts with the first drink. So never, ever drink and drive.

Here’s a great shortcut to estimate BAC - if you are a 220 lb man, one regular 12 ounce beer (or 5 oz of wine or 1.5 oz of spirits) will raise your BAC to .020 in one hour. If you weigh half of that (110 lbs) your BAC will be twice as much as (.040) in one hour with the same amount of alcohol. So if a 220 lb man shotguns 4 regular beers in a row, he will be at the “legal limit” of .080 BAC one hour later.

If you are a 260 lb woman then one regular 12 ounce beer will raise your BAC to .020 in one hour. If you weigh half of that (130 lb) one regular 12 ounce beer will raise your BAC to .040 in one hour. That means that two beers and you are at the legal limit!

In reverse, remember that it will take a little more than an hour for most people to go from a BAC of .020 to 0. Second, and most importantly, there is a BIG difference between what is a “legal” measurement and what is a safe state - impairment starts at the first drink, so never drink and drive!


Richard Hamilton, MD, FAAEM, FACEP, FACMT