What is the legal alcohol limit?

In the United States, the legal blood alcohol concentration (BAC) limit for driving is 0.08% for most drivers, with lower limits for commercial drivers and zero-tolerance laws for drivers under 21. ^[1][2] **Standard limit: 0.08% BAC ^[1][2] All 50 states and D.C. have a per se DUI law** at 0.08% BAC. This means that if your BAC is 0.08% or higher, you are legally presumed impaired — no other evidence of impairment is needed for a conviction. This standard was effectively nationalized when Congress conditioned federal highway funding on states adopting it (23 U.S.C. § 163). ^[1] Lower limits: - Commercial drivers (CDL holders) — 0.04% BAC under 49 C.F.R. § 392.5 ^[3] - Drivers under 21 — Most states have zero-tolerance laws setting the limit at 0.00%–0.02% for underage drivers - Utah — Uniquely set its limit at 0.05% BAC (the lowest standard in the nation as of 2019) "Impairment" even below the legal limit Even if your BAC is below 0.08%, you can still be charged with DUI/DWI if an officer observes signs of impairment (slurred speech, erratic driving, failed field sobriety tests). The 0.08% threshold is a *per se* limit, not a safe-to-drive limit. **How BAC is measured ^[2] Law enforcement uses breathalyzer tests (roadside and evidential), blood tests, and urine tests. Under implied consent laws**, refusing a chemical test typically results in automatic license suspension (commonly 1 year for first refusal) and may be used against you in court. The Supreme Court held in *Birchfield v. North Dakota* (2016) that police may administer breathalyzer tests incident to arrest without a warrant, but blood draws generally require a warrant. Approximate BAC at various consumption levels BAC is influenced by weight, sex, rate of consumption, and food intake. As a rough guide, for a 160 lb. adult male, one standard drink raises BAC approximately 0.02–0.03%. There is no guaranteed safe number of drinks before driving — the only safe BAC is 0.00%. *Never drink and drive. If in doubt, use a rideshare service or designate a sober driver.*