In all 50 U.S. states, you are legally considered under the influence of alcohol if your blood alcohol concentration (BAC) reaches 0.08% or higher. That’s the threshold for a standard DUI charge if you’re driving a passenger vehicle. But impairment begins well before that number, and several laws set the bar even lower depending on your age, your vehicle, and your state.
The 0.08% Standard and Its Exceptions
A BAC of 0.08% is the nationwide legal limit for drivers 21 and older operating a personal vehicle. Utah is the one exception: it lowered its limit to 0.05% in 2018, following a recommendation from the National Transportation Safety Board that a lower threshold would discourage people from driving after drinking at all.
Commercial drivers who hold a CDL are held to a stricter federal standard of 0.04%, roughly half the usual limit. And for anyone under 21, zero-tolerance laws in every state set the maximum BAC at less than 0.02%, which effectively means any detectable alcohol. Violating a zero-tolerance law typically results in an automatic license suspension.
It’s also important to know that you can be arrested below any of these thresholds. If a law enforcement officer observes impaired behavior, such as swerving, slurred speech, or poor coordination, that alone can be probable cause for a DUI arrest regardless of your BAC reading.
DUI, DWI, and Other Terms
States use different names for alcohol-related driving offenses, and the terminology can be confusing. DUI (driving under the influence) and DWI (driving while intoxicated) are the most common, but some states also use OUI (operating under the influence), OWI (operating while intoxicated), or DWAI (driving while ability impaired). In practice, all of these describe the same core offense: operating a vehicle while too impaired to do so safely.
Some states use these terms to distinguish severity. New York, for example, separates charges into tiers. A DWAI/alcohol charge applies when your BAC falls between 0.05% and 0.07%. A standard DWI kicks in at 0.08%. An aggravated DWI applies at 0.18% or above. These aren’t just different labels; they carry progressively harsher penalties. Other states treat DUI and DWI as interchangeable. The charges can also apply to impairment from prescription drugs, over-the-counter medications, or illegal substances, not just alcohol.
What Impairment Actually Feels Like at Each Level
The legal limit of 0.08% wasn’t chosen arbitrarily. It marks a point where measurable deficits in balance, vision, reaction time, and judgment are reliably present. But the effects of alcohol start much earlier than most people realize.
At a BAC of 0.02% to 0.04%, you’ll feel light-headed, relaxed, and warm. Your mood shifts, and your judgment is mildly impaired, though you probably won’t notice it. At 0.05% to 0.07%, the effects become more obvious: lower inhibitions, mild memory impairment, exaggerated emotions, and a noticeable “buzz.” This is the range where Utah considers you legally impaired and where New York’s DWAI charge begins.
At 0.08% to 0.10%, the legal threshold in most states, impairment is no longer subtle. Your balance is off, your speech may slur, your vision is affected, and your reaction time is measurably slower. Self-control and judgment are compromised. At 0.11% to 0.15%, the initial euphoria fades and alcohol’s depressive effects take over. Anxiety or unease may replace the earlier “high,” and gross motor control, the ability to walk steadily, coordinate your limbs, or perform basic physical tasks, is significantly impaired.
What Counts as One Drink
Understanding standard drink sizes helps you estimate how quickly your BAC might rise. According to the CDC, one standard drink is 12 ounces of beer at 5% alcohol, 5 ounces of wine at 12% alcohol, or 1.5 ounces of distilled spirits (a single shot) at 40% alcohol. Malt liquor falls in between: 8 ounces at 7% alcohol equals one drink.
The catch is that many real-world servings are larger than these standards. A typical restaurant pour of wine is often 6 to 8 ounces. A craft beer might be 7% or 8% alcohol instead of 5%. A strong cocktail can contain two or three shots. If you’re estimating your intake based on “number of drinks,” the actual alcohol consumed may be significantly more than you think.
How Fast Your Body Processes Alcohol
Your liver breaks down alcohol at a roughly fixed rate: about one standard drink per hour for an average-sized person (around 154 pounds). This translates to approximately 7 grams of pure alcohol per hour. That rate doesn’t speed up with coffee, food, or cold showers, and it varies from person to person based on body weight, liver health, sex, genetics, and how often you drink.
Because your body eliminates alcohol at a relatively constant pace, drinking faster than one drink per hour causes your BAC to climb. Two drinks in an hour will leave you with roughly one drink’s worth of alcohol still circulating by the time the hour ends. Three drinks in an hour puts you in a deeper deficit. This is why binge drinking raises BAC so quickly, and why “spacing your drinks” is more than a cliché.
How BAC Is Measured
Law enforcement uses three main tools to measure BAC: breath tests, blood draws, and urine tests. Roadside breathalyzers are the most common first step. They estimate your BAC based on the alcohol vapor in your exhaled breath. Blood tests, drawn at a police station or hospital, are considered more accurate and are often used as the evidentiary standard in court.
Both methods have limitations. Alcohol has a short detection window in breath and blood, meaning these tests only capture very recent drinking. A breath test can miss someone who drank heavily hours earlier but whose BAC has since dropped. Conversely, a breathalyzer reading taken shortly after your last sip may be temporarily inflated by residual alcohol in your mouth rather than reflecting your true blood level.
How Officers Assess Impairment on the Road
Before or alongside a breath test, officers typically administer standardized field sobriety tests. There are three approved by the National Highway Traffic Safety Administration. The first is the Horizontal Gaze Nystagmus test, where an officer moves an object (usually a pen or finger) in front of your eyes and watches for involuntary jerking of the eyeball, which becomes more pronounced with alcohol consumption. The second is the Walk and Turn test: you walk heel-to-toe along a straight line, turn, and walk back while the officer watches for balance problems, wrong number of steps, or inability to follow instructions. The third is the One Leg Stand, where you raise one foot about six inches off the ground and count aloud for 30 seconds.
These tests were developed through controlled studies and are designed to detect impairment at or above a BAC of 0.08%. They give officers evidence of impairment that exists independently of a breath or blood reading, which is one reason a person can be charged even with a BAC below the legal limit.