Estimate your blood alcohol content from what you drank, your body weight, and how much time has passed. This tool is for education only and cannot tell you whether you are fit to drive.
BAC Calculator
Estimate your blood alcohol content and how long alcohol may stay in your system.
How to Use This Calculator
Choose your gender and enter your body weight, then add the number of beers, glasses of wine, and measures of spirits you have had. Enter how many hours have passed since the first drink.
The tool applies the Widmark formula, the same model used in alcohol research for decades, and returns an estimated blood alcohol content along with a rough decline curve.
Treat every number as an approximation. The calculator has no way to know your pour sizes, what you ate, or how your liver works today, and all of those change the real answer.
What Is Blood Alcohol Content?
Blood alcohol content, usually shortened to BAC, measures how much alcohol is circulating in the bloodstream. It is written as a percentage, so a BAC of 0.08 means alcohol makes up eight hundredths of one percent of the blood.
Alcohol enters the bloodstream through the stomach and small intestine, then travels to the brain within minutes. That is why the effects arrive quickly and why they build as more drinks are added.
The liver then does the slow work of clearing it. Because absorption is fast and removal is slow, drinking faster than the liver can keep up is what pushes BAC upward.
How Is BAC Calculated?
The Widmark formula estimates BAC from four things: how much pure alcohol was consumed, body weight, a distribution constant based on body water, and time elapsed.
Body water matters because alcohol spreads through water, not fat. The formula uses roughly 0.73 for men and 0.66 for women, reflecting average differences in body composition. Someone with more body water dilutes the same alcohol more.
Time is then subtracted at a typical elimination rate of about 0.015 per hour. This is an average, and it is the part of the formula that varies most between people.
What Counts as One Standard Drink?
A standard drink in the United States contains about 0.6 fluid ounces, or roughly 14 grams, of pure alcohol. That is the unit this calculator counts.
In practice that means a 12 ounce beer at 5 percent, a 5 ounce glass of wine at 12 percent, or a 1.5 ounce measure of spirits at 40 percent. Each of those holds about the same alcohol despite looking very different.
This is where estimates go wrong most often. A craft beer at 8 percent, a generous home pour of wine, or a cocktail with two shots each count as more than one standard drink, and undercounting quietly understates BAC.
What Do the BAC Levels Mean?
Below 0.02, most people notice little, though subtle changes in judgement can already appear. Between 0.02 and 0.05, mood lifts, inhibition drops, and reaction time starts to slow.
From 0.05 to 0.08, coordination, tracking, and decision making are measurably worse. Much of Europe, Australia, and Canada set the driving limit at 0.05 for this reason. At 0.08 and above, a driver is over the legal limit across the United States, with clear loss of balance, speech clarity, and reaction speed.
Past 0.15, impairment becomes severe, with vomiting and blackouts common. Around 0.30 and higher, alcohol poisoning becomes a real danger, since alcohol suppresses the reflexes that control breathing.
How Long Does Alcohol Stay in Your System?
The liver clears alcohol at a fairly steady pace, roughly one standard drink per hour for many adults. That rate does not speed up no matter what else you do.
Because of that, a night of five or six drinks can take most of the following morning to clear. Someone who stops drinking at two in the morning may still have alcohol in their blood at breakfast, which is how many next-day driving offences happen.
Different tests also detect alcohol for different windows. Breath and blood tests reflect current levels, while urine tests can show evidence long after impairment has passed.
Why Does BAC Differ Between People?
Two people can drink the same amount on the same night and end up in very different states. Body weight and body composition explain part of it, since a larger body with more water dilutes alcohol further.
Food is another major factor. Drinking on an empty stomach sends alcohol into the bloodstream quickly, while a meal, especially one with fat and protein, slows absorption and blunts the peak.
Genetics, liver health, medication, hydration, sleep, and drinking history all play a role too. This variability is exactly why no formula can promise an accurate personal number.
Can You Sober Up Faster?
No. This is one of the most persistent myths about alcohol, and believing it puts people in danger.
Coffee, cold showers, fresh air, exercise, and greasy food do nothing to lower blood alcohol content. Caffeine may make someone feel more awake while leaving them just as impaired, which is arguably worse, because the feeling of alertness encourages bad decisions.
Only time allows the liver to finish its work. Water and food help with hydration and comfort, and they may ease a hangover, but they do not clear alcohol from the blood any faster.
What Is the Legal Driving Limit?
Limits vary widely. Most of the United States, England, and Wales use 0.08. Much of Europe, Australia, and Canada use 0.05, while Scotland uses 0.05 as well.
Many countries apply stricter rules to specific drivers. Learners, drivers under a certain age, and commercial drivers often face limits of 0.02 or effectively zero, and some countries set zero tolerance for everyone.
Anyone driving abroad should check local law rather than assume. Penalties in many places include immediate licence loss, heavy fines, and imprisonment.
Why Should You Never Use This to Decide About Driving?
A calculator works from averages, but you are not an average. The formula cannot see your actual pour sizes, your last meal, your medication, or how tired you are, and each of those shifts the real number.
Impairment also begins well below any legal threshold. Studies have found measurable declines in reaction time and attention at levels far under 0.08, which means being under a limit is not the same as being safe.
The only responsible approach is to separate drinking from driving completely. Plan the ride home before the first drink, and treat any alcohol at all as a reason not to drive.
How Does Alcohol Affect Long-Term Health?
Beyond a single night, regular drinking carries real risks. The liver takes the heaviest load, with fatty liver often appearing first, and continued heavy drinking can progress to inflammation and permanent scarring.
Alcohol also raises blood pressure, disrupts sleep architecture even when it helps you fall asleep, and is classified as a carcinogen linked to cancers of the breast, liver, colon, and oesophagus.
Health bodies including the NHS and the CDC advise keeping intake low, with several drink-free days each week. Anyone who finds cutting back difficult should speak with a doctor, since support is available and effective.
Frequently Asked Questions
How accurate is a BAC calculator?
It gives a rough estimate, not a measurement. The Widmark formula relies on averages for body water and elimination rate, and it cannot account for your food, medication, liver health, or true pour sizes. Real levels can be considerably higher or lower than shown, which is why the result must never guide a decision about driving.
How long does it take for BAC to reach zero?
The liver clears roughly one standard drink per hour, so a BAC of 0.08 takes over five hours to fall to zero. Nothing shortens that. Someone who drinks heavily late at night can still be over the limit the next morning, even after a full night of sleep.
Does eating food lower your BAC?
Food slows how quickly alcohol is absorbed, which lowers the peak and makes the rise gentler. It does not reduce the total amount of alcohol entering the blood or speed up how fast the liver clears it. Eating before drinking helps, but it never makes drinking and driving acceptable.
Can coffee or a cold shower sober you up?
No. Neither affects blood alcohol content at all. Caffeine can mask tiredness and make someone feel sharper while leaving them just as impaired, which can lead to worse decisions. Only time lowers BAC.
Does BAC keep rising after your last drink?
Yes, it often does. Alcohol already in the stomach and intestine continues to be absorbed, so levels can keep climbing for 30 to 90 minutes after the final drink. Someone who feels fine when they stop may be more impaired half an hour later.
Is it safe to drive under the legal limit?
Legal is not the same as safe. Reaction time, attention, and judgement decline at levels well below 0.08, and crash risk rises from the first drink. Legal limits mark the point of prosecution, not the point where impairment begins. The safest amount before driving is none.
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Medical Disclaimer: This calculator and article are for general informational purposes only and do not constitute medical, legal, or safety advice. BAC estimates are approximations based on averages and may differ substantially from actual blood alcohol content. This tool must never be used to decide whether to drive or operate machinery. If you are concerned about your drinking, speak with a doctor. If you suspect alcohol poisoning, contact emergency services immediately.