A blood alcohol level (also called blood alcohol concentration, or BAC) is considered high at 0.08% or above, which is the legal limit for driving in 49 U.S. states. But impairment starts well before that number, and levels above 0.30% can be life-threatening. Understanding what these percentages actually mean for your body helps put the numbers in context.
How BAC Is Measured
BAC is expressed as a percentage of alcohol in your blood by volume. A BAC of 0.08% means there are 0.08 grams of alcohol per 100 milliliters of blood. That sounds tiny, but alcohol is potent: even small concentrations measurably affect your brain, coordination, and judgment.
In the United States, one standard drink contains 0.6 ounces (14 grams) of pure alcohol. That’s 12 ounces of regular beer at 5% alcohol, 5 ounces of wine at 12%, or a 1.5-ounce shot of 80-proof liquor. Each of these raises your BAC by a roughly similar amount, though exactly how much depends on your body.
BAC Levels and What They Feel Like
The effects of alcohol follow a fairly predictable curve as BAC rises. Here’s what happens at each stage:
- 0.02%: Slight mood changes, relaxation, and a minor dip in judgment. You may feel warm. Your ability to track moving objects with your eyes starts to decline.
- 0.05%: Lowered alertness, reduced inhibition, and impaired judgment. Fine motor control slips, making it harder to focus your eyes precisely. Most people feel noticeably loosened up at this level. Utah sets its legal driving limit here.
- 0.08%: Muscle coordination becomes poor, affecting balance, speech, vision, and reaction time. Short-term memory, reasoning, and self-control are all impaired. This is the legal driving limit in every other U.S. state.
- 0.10%: Clear deterioration in reaction time. Speech is slurred, thinking slows, and coordination worsens. Drivers at this level struggle to stay in their lane or brake appropriately.
- 0.15%: Far less muscle control than normal, significant loss of balance, and vomiting is common (unless the person has built up a high tolerance or reached this level very gradually). At this point, driving ability is substantially impaired across the board.
For drivers under 21, every U.S. state sets the legal limit at 0.02% or lower, essentially a zero-tolerance policy. Some states also impose limits of 0.02% or 0.04% for people with prior impaired-driving convictions.
When BAC Becomes Dangerous
Above 0.15%, you’re moving from “very drunk” into medically dangerous territory. The body’s protective reflexes, like gagging to prevent choking on vomit, start to weaken. At 0.20% and beyond, most people are severely disoriented and may need help walking or staying conscious.
A BAC over 0.31% is especially dangerous. At this range, you may lose consciousness, have trouble breathing, or slip into a coma. The body’s ability to regulate basic life functions, including heart rate and breathing, becomes suppressed. A BAC above 0.40% carries a serious risk of death. The range between 0.31% and 0.45% is considered life-threatening, and many people in this range are experiencing what clinicians classify as alcohol overdose (alcohol poisoning).
These numbers aren’t absolute cutoffs. A person with no tolerance could face a medical emergency at a lower BAC than someone who drinks heavily. But at 0.30% and above, the danger is real for everyone.
Why the Same Drinks Hit People Differently
Two people can drink the same amount and end up with very different BAC readings. The biggest factors are body weight, biological sex, how quickly you drank, and whether you’ve eaten recently.
Larger bodies have more water to dilute alcohol, so a 200-pound person will generally reach a lower BAC than a 130-pound person after the same number of drinks. Women typically reach higher BAC levels than men of the same weight because women tend to carry proportionally less body water and more body fat, and fat doesn’t absorb alcohol the way water does. Drinking on an empty stomach also sends alcohol into your bloodstream faster, producing a sharper spike in BAC.
Genetics play a role too. The enzyme your liver uses to break down alcohol varies in efficiency from person to person. Some people metabolize alcohol more slowly, meaning it accumulates faster in their blood even at a moderate drinking pace.
How Fast Your Body Clears Alcohol
Your liver breaks down alcohol at a remarkably steady rate: about 0.015% BAC per hour. That rate doesn’t change much regardless of how much you’ve had. Coffee, food, water, or cold showers won’t speed it up.
To put that in practical terms: if your BAC is 0.08% and you stop drinking, it will take roughly five and a half hours for your body to return to 0.00%. At a BAC of 0.15%, you’re looking at about ten hours. This is why people can still be legally impaired the morning after a night of heavy drinking.
At very high BAC levels, the math gets sobering. A BAC of 0.30% would take approximately 20 hours to clear entirely. During that time, the person remains at risk for complications including aspiration (inhaling vomit), respiratory depression, and loss of consciousness.
Signs of Alcohol Poisoning
You can’t measure someone’s BAC by looking at them, but certain symptoms signal a dangerously high level. Vomiting while semiconscious or unconscious is one of the clearest warning signs, because the person may not be able to clear their airway. Slow or irregular breathing (fewer than eight breaths per minute, or gaps of ten seconds or more between breaths) indicates the brain’s respiratory centers are being suppressed. Pale or bluish skin, seizures, and an inability to be woken up are all emergencies.
A common and dangerous mistake is assuming someone who has passed out from drinking just needs to “sleep it off.” BAC can continue to rise after the last drink, especially if the person drank a large amount quickly. Alcohol in the stomach keeps absorbing into the bloodstream even after someone stops drinking or loses consciousness.