BAC stands for blood alcohol concentration (sometimes called blood alcohol content or blood alcohol level). It measures the amount of alcohol currently in your bloodstream, expressed as a percentage. A BAC of 0.08%, for example, means there are 0.08 grams of alcohol per 100 milliliters of blood. This single number is used in medicine, law enforcement, and public health to gauge how intoxicated a person is.
How BAC Is Measured
There are two common ways to measure BAC. A blood draw gives the most accurate result, reported as a percentage (like 0.08%) or in grams per milliliter. A breathalyzer estimates BAC by measuring alcohol vapor in your exhaled breath, then converting that reading using a standard ratio.
Breathalyzers are convenient but not perfectly precise. In a study of over 400 paired breath and blood samples collected from drivers in Wisconsin, breathalyzer readings came in lower than the actual blood result by more than 0.01% about 61% of the time. They matched within 0.01% roughly a third of the time, and read higher only 6% of the time. This is why law enforcement sometimes follows up a roadside breath test with a blood draw when accuracy matters in court.
What Different BAC Levels Feel Like
BAC effects follow a fairly predictable progression, though individual tolerance varies. The National Highway Traffic Safety Administration breaks it down this way:
At 0.02%, most people feel slightly relaxed and warm. Mood shifts a little, and the ability to track a moving object starts to decline. At 0.05%, behavior becomes more exaggerated, inhibitions drop, and small-muscle control suffers. You may have trouble focusing your eyes or steering a vehicle smoothly.
At 0.08%, the legal limit in most U.S. states, coordination is clearly impaired. Balance, speech, vision, and reaction time all deteriorate. Judgment, self-control, and short-term memory are affected, and it becomes harder to detect danger or process new information quickly.
At 0.10%, reaction time and motor control are noticeably degraded. Speech slurs, thinking slows, and maintaining a lane while driving becomes difficult. By 0.15%, muscle control is far below normal, balance is severely compromised, and vomiting is common unless tolerance is unusually high.
Above 0.15%, the risks escalate sharply. At very high levels, alcohol can suppress automatic brain signals that control breathing and the gag reflex. Blackouts, loss of consciousness, and death become real possibilities.
Legal BAC Limits
In the United States, every state sets the illegal per se limit at 0.08%, with one exception: Utah lowered its limit to 0.05% in 2018. For drivers under 21, all states enforce a near-zero tolerance policy of 0.02% or lower.
Other countries set their own thresholds. Scotland lowered its limit from 0.08% to 0.05% in 2014, aligning with most of continental Europe. Many countries in Asia, Eastern Europe, and South America enforce even stricter limits, with some requiring a BAC of exactly zero for all drivers.
What Affects Your BAC
Two people can drink the same amount of alcohol and end up with very different BAC readings. Several biological and situational factors explain why.
Body weight and composition: A smaller person generally reaches a higher BAC from the same number of drinks because alcohol distributes through a smaller volume of body water. Biological sex: Women tend to reach higher peak BAC levels than men given the same dose, partly because of differences in body composition and enzyme activity. Food in the stomach: Eating before drinking has a significant buffering effect. Research on healthy volunteers found that a high-energy meal reduced overall alcohol absorption compared to a low-energy meal. Interestingly, meal composition mattered too: high-protein meals produced the lowest peak BAC, while high-fat meals produced the highest among the food types tested.
The concentration of the alcoholic drink and how quickly you consume it also play a role. Drinking the same total amount of alcohol in a concentrated form over a short period pushes BAC up faster than sipping a diluted drink over several hours.
How Fast Your Body Clears Alcohol
Your liver does the heavy lifting when it comes to processing alcohol. For an average-sized adult (around 154 pounds), the body eliminates roughly 7 grams of alcohol per hour. That translates to about one standard drink per hour. In the United States, a standard drink contains 14 grams of pure alcohol, which is the amount in a 12-ounce beer, a 5-ounce glass of wine, or a 1.5-ounce shot of distilled spirits.
This means if you stop drinking at a BAC of 0.08%, it will take roughly four to five hours for your body to return to zero. There is no reliable way to speed this up. Coffee, cold showers, and exercise do not meaningfully accelerate alcohol metabolism. The sugar fructose has been shown in laboratory settings to modestly increase the rate of alcohol breakdown, but not enough to make a practical difference in real-world situations. Time is the only thing that consistently lowers your BAC.
Alcohol Poisoning and Dangerous Levels
Binge drinking, defined as reaching a BAC of 0.08% or higher in a single session, is where serious health risks begin to climb. But the truly dangerous territory starts well above that. As BAC rises past 0.15% and approaches 0.20% or higher, the body’s protective reflexes start shutting down. The gag reflex may stop working, which means a person who vomits while unconscious can choke. Breathing can slow dangerously or stop altogether.
Signs of alcohol poisoning include confusion, vomiting, seizures, slow or irregular breathing, pale or blue-tinged skin, and an inability to stay conscious. A person does not need to show all of these symptoms to be in danger. BAC can also continue to rise after someone stops drinking, because alcohol in the stomach and intestines is still being absorbed into the bloodstream. This is why someone who “just passed out” can deteriorate further without drinking another drop.