There is no exact answer to determine how much you have to drink to reach the legal limit for driving or flying. However, there is a way to approximate whether you are approaching the legal limit in your state (usually 0.08 blood alcohol level) based on your weight, how much you have had to drink, and how long you have been drinking.  For example:

  • If you are around 100 lbs., you can generally only have about one serving of alcohol before being over 0.08, and only two servings before being above 0.1 (for those states where the legal limit 0.1)
  • However, a person is closer to 160 lbs. can have about 3 servings of alcohol and still be below the legal limit for driving

A good rule of thumb to use is that no matter what your weight is, if you have had three servings of alcohol in rapid succession you are most likely over the legal limit for blood alcohol level when driving.

Your blood alcohol level will also depend on how much time you have spent drinking. If you have a spaced your drinks out over a lengthy period of time, such as the span of a few hours, your blood alcohol level is going to be significantly lower than if you had the same amount of drinks in the span of one hour. Generally, you can subtract 0.01% from your estimated blood alcohol level for each 40 minutes that go by while drinking.

What Is 1 Serving of Alcohol?

Keep in mind the amount of alcohol that constitutes 1 serving differs depending on the type of drink.  For example, 12 oz. of hard liquor is a far greater amount of alcohol than 12 oz. of beer, and as a result will have a much greater impact on your blood alcohol level. Generally, the rule is 1 serving of alcohol is equal to 1 oz. of 100 proof liquor, a 12 oz. beer, or 4 oz. of table wine.

What Are Some Other Factors that Affect a Person’s Blood Alcohol Level?

Though the amount of drinks, the drinker’s weight, and the time between drinks tend to play the largest roles in estimating a person’s blood alcohol level, there are some other factors that can play a role as well:

  • Fatigue: exhaustion can significantly increase a person’s blood alcohol level when they are drinking. Keep in mind, even if you have not had much to drink, fatigue can adversely affect your judgment just as alcohol can
  • Medications: some types of medications can have adverse side affects when taken with alcohol, so be sure to check the warning labels on any medications (prescriptive or over the counter) you take
  • Food: drinking on an empty stomach can increase your blood alcohol level significantly more than if you been eating before or while you were drinking

If I Have Been Arrested for Drunk Driving, What Should I Do?

Contact a criminal defense attorney or a DUI lawyer immediately. Your attorney will be able to advise you of your rights and help you with any possible defenses you may have. Keep in mind that the criminal justice system can be rather complex and confusing, so an attorney can help guide you through it and help you pick out a path that is in your best interests.