Blood Alcohol Concentration (BAC) refers to the percent of alcohol (ethyl alcohol or ethanol) in a person’s bloodstream and is usually determined by a breathalyzer test or a blood test when the police suspect a driver of being intoxicated. For example, a BAC of .10% means that the person’s blood supply contains one part alcohol for every 1,000 parts blood.

In most states a driver is considered legally intoxicated if their BAC is .08 or higher. This BAC level is generally prescribed by a state statute (a law enacted by the state legislature) and creates a presumption of intoxication—also known as per se BAC because it is intoxication by definition. In Utah, the per se BAC level is .05.

Most states have a zero-tolerance BAC level of .02 for drivers under the legal drinking age (usually 21) that will result in a DUI/DWI charge. And most states also have an enhanced penalty or aggravated DUI/DWI charge for drivers whose BAC is .15 or higher—with a few states placing this aggravated or enhanced-penalty DUI/DWI BAC level at .16 to .20.

In Michigan, the legal limit for Blood Alcohol Concentration (BAC) for drivers 21 years and older is .08%, in line with the majority of states. This means that a driver with a BAC of .08% or higher is considered legally intoxicated and can be charged with Operating While Intoxicated (OWI). Michigan also adheres to a zero-tolerance policy for drivers under the age of 21, where a BAC of .02% or more can result in a charge of Operating While Visibly Impaired (OWVI). For commercial drivers, the BAC limit is lower, set at .04%. Additionally, Michigan imposes enhanced penalties for drivers who are caught with a BAC of .17% or higher, which is considered a 'High BAC' offense and can lead to more severe consequences under the state's 'Super Drunk' law.