The level of blood alcohol content (BAC) at the time of driving is used as evidence that a person was driving while intoxicated (DUI). It is illegal in all states to drive if your BAC level is 0.08% or higher. If you’re a minor, then the legal limit is 0.02%. Because BAC establishes whether a person is guilty of DUI and also the severity of penalties in some states, getting an accurate reading is imperative.

Determining BAC

If you’re pulled over by a police officer for a DUI, the officer will likely request that you blow into the breathalyzer to get a BAC reading for you. A breathalyzer attempts to measure the amount of alcohol expelled by the air in your lungs. The alcohol in the air you breathe out is assumed to be at the same concentration as the alcohol in your blood. However, many people have shown that the results of a breathalyzer test are very often inaccurate. Find out more about flaws in breathalyzer testing. The other way to gauge BAC is using a blood test. Blood is drawn from the subject (usually at the police station after arrest), which is then tested for the amount of alcohol in it. Blood tests are almost always more accurate than breath tests since the alcohol is measured directly from the subject's blood instead of secondhand from the subject’s breath. This doesn’t mean that blood tests are infallible, however. Read more on blood tests.

DUI Penalties

In some states, there is only one level of penalty if you register a BAC level of 0.08% or more in a DUI as a first time offender. Penalties will vary depending on which state you’re in, so be sure to check your particular state’s laws. DUI penalties can look something like this for a first conviction:

  • Possible jail time (max. of 1 year)
  • Fines: $300 - $2500
  • Mandatory substance abuse program attendance
  • Driver license suspension of 60-90 days

Graded DUI Charges/Penalties Based on BAC

Other states have graded levels of DUI charges depending on your BAC level, which will determine the specific severity of consequences if you’re convicted. This means that if your BAC level is extremely high, then your penalty will also be much worse than it would be if you had a lower BAC level. These states typically have three tiers of DUI charges. Each state’s laws have variations, so your state may have slightly different penalties or definitions. Keeping that in mind, here’s a typical breakdown of how a state with three tiers of DUI offenses often defines them (for first time convictions). General impairment: BAC between 0.08% and 0.099% A general impairment DUI charge usually counts as a misdemeanor and tends to carry relatively light penalties, such as fines less than $500, probation ranging from six months to a year, and substance abuse program attendance. High rate of BAC: BAC ranges from 0.10% to 0.159% A high rate DUI charge has somewhat more serious penalties associated with it. Penalties in different states can approximate these: driver license suspension for a year, jail time anywhere from 2 days to 6 months, fines ranging from $500 to $5000, and substance abuse program attendance. Highest rate of BAC: BAC is 0.16% or more Penalties for highest rate BAC charges can include driver license suspension for a year, jail time of 3 days to 6 months, fines ranging from $1000 to $5000, and substance abuse program attendance. Always remember that DUI punishments vary state to state, so check your state’s laws regarding definitions and sentencing.