Impacts of Underaged Drinking

Measuring How Much You Drank: Blood Alcohol Content (BAC)

Blood alcohol content or blood alcohol concentration (BAC) is the amount of alcohol in a person’s blood. BAC is primarily used as a measurement of intoxication for legal or medical purposes.

The concentration of alcohol in the blood continues to rise even after drinking has stopped because alcohol in the stomach continues to enter the blood stream.

A standard drink is:


12-ounce can or bottle of regular beer


5-ounce glass of wine

martini drinks

A shot or 1.5 ounces of 80 proof liquor such as vodka, tequila, or rum, either alone or in a mixed drink

The number of drinks an adolescent or an adult has is a poor measure of BAC because of variations in weight and sex of the person who is drinking. One standard drink (on average 14 grams) of alcohol will increase the average person’s BAC roughly 0.02% to 0.05%, so two drinks may cause driving impairment.

Each state has individual laws for punishing drivers who operate motor vehicles with an elevated BAC reading. Laws in 50 states and the District of Colombia consider a person legally intoxicated if their BAC is 0.08% or higher.

Mixing alcohol with carbonated drinks will speed up the absorption of alcohol into the blood stream. For teens, this is particularly significant, since they often prefer sweeter, mixed drinks.

If a person is not an experienced drinker, a lower BAC will affect them more than someone who has built up a tolerance. A blood alcohol content of 0.40% will typically kill about half of all adults.

Because blood alcohol concentration continues to rise even after drinking has stopped, there is only one thing that lowers BAC, and that is time. Coffee and cold showers may make a driver more alert but will not lower BAC or make it safe to drive.

Impairments usually occur once an individual’s BAC level reaches 0.05%. Potential problems at this BAC level include:

  • Slowed eye movements
  • Changes in what you see and in reaction time
  • Trouble with certain types of steering tasks
  • Difficulty processing information.

Next: Binge Drinking / Alcohol Poisoning