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What is a standard drink and how much alcohol is in one?

To be charged with a DUI, a driver must be found to be under the influence of alcohol. This determination is made by measuring the amount of alcohol in a person's system, typically with a breath or blood test. In most cases, a driver with a blood alcohol content over .08 percent is legally drunk, and cannot drive a motor vehicle. In some cases, a driver can be charged with a DUI if he has a BAC lower that .08, notably if he is a commercial driver or if he is under 21 years old.

How alcohol is measured in the body
Measuring alcohol intake is similar to understanding BAC. The National Institute on Alcohol Abuse and Alcoholism (NIAA) determined a method of measuring intake called the standard drink. The NIAA defines the standard drink as any alcoholic beverage that contains 0.6 fluid ounces of alcohol. This means that the higher the alcohol percentage of alcohol in the drink, the less volume is required to elevate a person's BAC.

What makes a standard drink?
The NIAA says that a standard drink consists of 0.6 fluid ounces of alcohol. To compare, standard drinks include:

  • 12 fluid ounces of beer
  • 5 fluid ounces of wine
  • 1.5 fluid ounces of 80 proof liquor.

The alcohol content in hard liquor, like whiskey, vodka and gin, is often described as a "proof" level. To determine a liquor's alcohol percentage, simply divide the proof number by two. A bourbon that is labelled as 90 proof, for instance, is 45 percent alcohol.

Remember that while the term "standard drink" suggests a single drink in a bar, in many cases, mixed drinks include more alcohol than is in an official standard drink.

How many standard drinks?
Although one can measure blood alcohol content and assess alcohol intake in percentages and standardized terms, a number of variables affect the way a body processes alcohol. There is no tried and true way to determine the number of standard drinks that will elevate a person's BAC to a certain level. Alcohol absorption is affected by ethnicity, gender, genetics and the amount of food consumed prior to drinking.

Hard alcohol, like whiskey or vodka, will typically be absorbed faster than beer because the concentration of alcohol is greater in liquor than it is in drinks with a lower alcohol volume.