In the United States, a blood alcohol concentration (BAC) of 0.08% is the legal threshold for drunk driving in all 50 states. But impairment starts well before that number, and the physical experience most people associate with being “drunk” can show up anywhere from 0.05% to 0.15% depending on your body and your drinking history.
BAC is measured as a percentage of alcohol in your blood by weight. A BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood. That sounds tiny, but the brain is remarkably sensitive to alcohol, and even small increases in BAC produce measurable changes in coordination, judgment, and reaction time.
The Legal Line: 0.08% in Every State
Every U.S. state sets the legal limit for drivers 21 and older at 0.08%. Cross that threshold and you can be charged with driving under the influence, regardless of whether you feel impaired. For drivers under 21, most states enforce a zero-tolerance policy, meaning any detectable amount of alcohol is illegal.
The 0.08% standard is relatively recent. Just a few decades ago, some states set the limit at 0.15%. It gradually dropped to 0.12%, then 0.10%, before settling at the current number. More than 100 countries now use a 0.05% limit, and there has been ongoing discussion about whether U.S. states should follow.
What Each BAC Level Actually Feels Like
The National Highway Traffic Safety Administration breaks impairment into stages, and the progression is steeper than most people expect.
At 0.02%, the effects are subtle. You may feel slightly warmer, more relaxed, and in a mildly altered mood. Your ability to track a moving object with your eyes declines, and multitasking becomes slightly harder. Most people would not describe themselves as “drunk” at this level, but measurable changes are already underway.
At 0.05%, behavior becomes exaggerated. Alertness drops, inhibitions loosen, and small-muscle control starts to slip, making it harder to focus your eyes. Judgment is noticeably impaired. Steering becomes more difficult, and your ability to respond to sudden driving emergencies is reduced. This is the level where many countries draw the legal line.
At 0.08%, coordination is clearly affected. Balance, speech, vision, reaction time, and hearing all decline. You have a harder time detecting danger, reasoning through problems, and controlling your speed. Short-term memory starts to fail. This is the point where U.S. law says you are legally intoxicated.
At 0.10%, deterioration is obvious to anyone watching. Speech is slurred, thinking is slow, and reaction time is significantly delayed. Staying in a lane while driving and braking at the right moment become unreliable.
At 0.15%, muscle control is far below normal. Balance is seriously compromised, and vomiting is common unless you reached this level very slowly or have a high tolerance. At this point, operating a vehicle safely is essentially impossible.
When Alcohol Becomes Dangerous
Between 0.15% and 0.30%, confusion, drowsiness, and repeated vomiting set in. This range is where people begin to lose awareness of their surroundings and may have difficulty staying conscious.
Between 0.30% and 0.40%, the risk of alcohol poisoning is high. Loss of consciousness is likely, and the body’s ability to maintain basic functions like breathing and temperature regulation starts to fail. This range is considered life-threatening. Deaths from alcohol overdose typically occur in this window or above it.
How Many Drinks Get You to 0.08%
A standard drink in the U.S. contains about 14 grams of pure alcohol. That equals a 12-ounce beer at 5% alcohol, a 5-ounce glass of wine at 12%, or a 1.5-ounce shot of spirits at 40%.
For a 150-pound man, roughly four standard drinks will push BAC to about 0.10%. A 150-pound woman drinking the same amount will typically reach about 0.12%. The difference comes down to body composition: women generally carry a higher percentage of body fat and less water per kilogram of body weight, and they produce less of the stomach enzyme that breaks down alcohol before it enters the bloodstream. Since alcohol distributes through water in the body, less water means a higher concentration from the same amount of drinking.
These are averages. Your actual BAC after a given number of drinks depends on your weight, body fat percentage, how quickly you drank, whether you ate beforehand, and how hydrated you are.
How Fast Your Body Clears Alcohol
The liver processes alcohol at a remarkably steady rate: roughly one standard drink per hour. This rate barely changes regardless of how much you’ve had. Coffee, cold showers, and food do not speed it up.
If you reach a BAC of 0.08% after four drinks over an hour, it will take approximately four to five hours for your BAC to return to zero. This is why people can still be over the legal limit the morning after heavy drinking.
Tolerance Does Not Equal Safety
People who drink heavily often believe they can “handle” more alcohol without becoming impaired. Research from the University of Chicago tested this directly. People with alcohol use disorder did show less impairment than light drinkers on fine motor and cognitive tasks at a BAC of 0.08% to 0.09%, the legal threshold.
But at the higher doses these drinkers were actually accustomed to (seven to eight drinks, producing a BAC around 0.13%), their impairment more than doubled compared to the standard dose. It never returned to baseline even after three hours. Their impairment at this level actually exceeded that of light drinkers at the lower dose. In other words, tolerance may mask the feeling of being drunk at moderate levels, but the physical effects accumulate regardless. Experienced drinkers who consume at their usual pace end up more impaired, not less.
Breathalyzers vs. Blood Tests
If you’re pulled over, you’ll likely encounter a handheld breathalyzer first. These devices estimate BAC from the alcohol in your breath, but they tend to read lower than the actual alcohol concentration in your blood. One large study of nearly 1,900 roadside tests found that breath readings underestimated true BAC by about 15% on average, with substantial random variation from person to person. A blood draw is more accurate and is typically what holds up in court, but the breathalyzer result is enough to establish probable cause for an arrest.
The practical takeaway: if a breathalyzer shows you at 0.08%, your actual blood alcohol may well be higher.