A blood alcohol concentration (BAC) of 0.08% is the legal threshold for impaired driving in most of the United States, but levels are generally considered medically high starting around 0.15% to 0.20%, where serious physical and cognitive impairment sets in. Above 0.30%, the risk of coma and death rises sharply. Understanding where you fall on this scale matters because the gap between “legally drunk” and “dangerously drunk” is smaller than most people think.
How BAC Is Measured
BAC represents the percentage of alcohol in your bloodstream. A reading of 0.10% means there is one part alcohol for every 1,000 parts of blood. The most common test measures this ratio directly from a blood sample and can detect alcohol for up to 12 hours after drinking. Breathalyzers estimate the same number using the alcohol vapor in your lungs.
Legal Limits Across the U.S.
Every state sets the legal per se limit for driving at 0.08%, with one exception: Utah lowered its limit to 0.05% in 2018. Colorado and New York also have “driving while ability impaired” laws that can penalize drivers below 0.08%, and West Virginia can revoke a license above 0.05%. For drivers under 21, all states set the limit at 0.02% or lower. If you’ve had a prior DWI conviction, some states drop your personal limit to 0.02% or 0.04%.
These numbers are legal boundaries, not safety thresholds. Measurable impairment in reaction time, judgment, and coordination begins well below 0.08%.
What Happens at Each BAC Range
At 0.02% to 0.05%, you may feel relaxed and slightly less inhibited, but most people can still function relatively normally. Fine motor skills and judgment start to slip, even if you don’t feel it.
At 0.08% to 0.15%, impairment becomes obvious. Balance, speech, reaction time, and decision-making all deteriorate significantly. This is the range where most alcohol-related car crashes occur.
At 0.15% to 0.30%, the situation becomes medically serious. Breathing may become inadequate, you may be unable to walk without help, and loss of bladder control or consciousness is likely. Confusion, vomiting, and extreme drowsiness are common. This range is where the term “high BAC” applies in a clinical sense.
Above 0.30%, the body’s basic survival functions are at risk. Breathing can slow to fewer than eight breaths per minute, body temperature drops dangerously low, and the gag reflex may shut down, meaning a person who vomits while unconscious can choke to death. Coma and fatal respiratory failure become real possibilities.
Signs of Alcohol Overdose
A high BAC can tip into alcohol poisoning, which is a medical emergency. The warning signs include mental confusion or stupor, inability to wake someone up, seizures, slow or irregular breathing (fewer than eight breaths per minute, or gaps of ten seconds or more between breaths), slow heart rate, clammy skin, bluish skin color, and extremely low body temperature. Vomiting while semiconscious is particularly dangerous because without a functioning gag reflex, the airway can become blocked.
Someone showing these signs needs emergency medical attention. Alcohol continues absorbing into the bloodstream even after a person stops drinking, so BAC can still be rising when someone passes out.
Why the Same Drinks Hit People Differently
Two people can drink the same amount and reach very different BAC levels. Several biological factors explain this.
Body size and composition play a major role. Alcohol dissolves in water, not fat, so a person with less body water (whether from smaller size or higher body fat percentage) will reach a higher BAC from the same number of drinks.
Sex makes a significant difference beyond body size. Women generally reach higher BAC levels than men even when matched for weight, partly because women’s stomachs don’t produce a key enzyme that breaks down about 30% of alcohol before it reaches the bloodstream. Men’s stomachs actively metabolize a portion of alcohol on contact; in women, that gene is effectively switched off, so more alcohol passes directly into the blood.
Genetics also matter. Roughly half of people of East Asian descent inherit a gene variant that produces a nonfunctional version of the enzyme responsible for clearing a toxic alcohol byproduct. This can cause that byproduct to build up to levels 20 times higher than normal, producing intense flushing, nausea, and rapid heartbeat, sometimes even at modest BAC levels.
How Fast Your Body Clears Alcohol
The average person metabolizes alcohol at a rate of roughly one standard drink per hour. For someone weighing about 154 pounds (70 kg), that works out to eliminating approximately 7 grams of alcohol per hour. This rate is mostly fixed. Coffee, food, water, and cold showers do not speed it up.
This means if you reach a BAC of 0.20%, it will take roughly 12 to 14 hours for your body to return to 0.00%. A person who stops drinking at midnight after a heavy night may still be legally impaired the next morning. This slow clearance rate is one reason high BAC is so dangerous: once you’re there, you’re stuck there for hours, and medical complications can develop during that window.
What Counts as Binge Drinking
The National Institute on Alcohol Abuse and Alcoholism defines binge drinking as a pattern that brings BAC to 0.08% or above. For a typical adult, that corresponds to five or more drinks for men, or four or more drinks for women, in about two hours. This is the most common form of excessive drinking in the U.S., and it’s the fastest route to a dangerously high BAC. Because the body can only clear about one drink per hour, consuming four or five in a short window creates a steep upward climb that can easily overshoot into the 0.15% to 0.20% range.