what bac indicates that a person is legally impaired?

In most of the United States, a blood alcohol concentration (BAC) of 0.08% or higher is what indicates a person is legally impaired for standard adult drivers.

Key legal BAC limits

• For drivers age 21 and over in most U.S. states: driving at 0.08% BAC or above is illegal and considered per se impaired.

• Utah is stricter and sets the legal limit at 0.05% BAC for adult drivers.

• Many places treat anything above about 0.05% as clear legal evidence of at least “impairment,” even if full “intoxication” is defined at 0.08%.

Important nuance

• A person’s driving can be measurably impaired below the legal limit; performance on driving-related tasks worsens at relatively low BAC levels, even when BAC has not yet reached 0.08%.

• Some jurisdictions also have zero-tolerance limits for drivers under 21, where any detectable BAC (for example, as low as 0.02%) can be a violation.

So, strictly legally, 0.08% is the common threshold for being presumed impaired while driving, but safety problems start at lower levels, and local laws can be stricter.