Before the numbers. If you are on this page at half past eleven with your keys in your hand, here is the honest answer first, before any arithmetic: nobody can tell you from a form that you are fit to drive, and this page is not going to pretend otherwise. What it can do is something more useful. It can show you how much alcohol was actually in the drinks you had, which is almost always more than people think, and it can tell you roughly how long it will be before that alcohol is gone. Get a ride tonight, and use the timing to plan tomorrow. That is the question this calculator is built to answer well.
How this BAC calculator works, and why it asks about your actual drinks
Most blood alcohol calculators ask you for a number of "drinks" and quietly multiply it by 14 grams. That works perfectly if every drink you had was a 12 oz beer at 5%, and it fails badly the moment one of them was not. A 16 oz pour of a 7% IPA is 1.87 standard drinks. A restaurant wine pour is often 8 oz of something near 13.5%, which is 1.8. A drink poured at home tends to be a double, which is 2. Count four of those as "four drinks" and you can be off by a factor of two, in the direction that gets people killed.
So this one asks what you actually drank. Pick the drink, say how many, and override the size or the strength when your glass was not standard. Every row is converted to grams of pure alcohol from its own volume and ABV, and the page shows you the standard drink equivalent for each row, because that conversion is the single most useful thing on this page. Then it runs the Widmark equation, the same one used in forensic toxicology, but with one important difference from every other calculator: it runs the whole published range of the constants instead of pretending there is one right answer.
The formula
BAC% = ( grams ÷ ( body weight in grams × r ) ) × 100 − elimination rate × hours since the first drink
r is the Widmark distribution ratio, the fraction of your body that behaves like water as far as alcohol is concerned. It averages 0.68 in men and 0.55 in women, and Widmark's own controlled experiments put the spread at plus or minus 0.17 for men and 0.11 for women, so we run 0.51 to 0.85 for men and 0.44 to 0.66 for women. Elimination rate is how fast your liver clears alcohol, commonly quoted as one figure of 0.015% per hour and actually varying from roughly 0.012 to 0.020% per hour in ordinary drinkers, so we run that band too. The low end of r paired with the low end of elimination gives the high BAC estimate. That is the one we put in the headline.
Note what those two ranges do to the answer. A man and a woman of the same weight who drink the same thing can differ by a third. Two men of the same weight can differ by two thirds, because one of them carries more water than the other. Any calculator that hands you a single number to three decimal places is telling you something it does not know.
Worked example: four beers, or eight?
A 160 lb man has four 16 oz craft IPAs at 7% ABV over an evening. It is 3 hours since the first one and 1 hour since the last.
Each IPA is 16 × 0.07 × 29.5735 × 0.789 = 26.13 g of alcohol, so four of them are 104.53 g, which is 7.47 standard drinks, not four.
His body weight is 160 × 453.59 = 72,575 g. At the low end of r: 104.53 ÷ (72,575 × 0.51) × 100 = 0.282%, less 3 hours at 0.012 = 0.246%. At the middle: 0.212% less 0.045 = 0.167%. At the high end of r and the fast end of elimination: 0.109%.
So the honest answer is 0.109% to 0.246%, and every point in that range is over the legal limit in all fifty states. The last drink was only an hour ago, inside the window in which blood alcohol is still climbing, so the page headlines that top figure as where he is heading rather than where he is: 14 hours 23 minutes before the high estimate falls under 0.08%, and 21 hours before it reaches zero.
Here is why this page was rebuilt. Type "4 drinks" into an ordinary BAC calculator with the same weight and the same 3 hours and it returns 0.068%, under the limit, with a green tick next to it. The drinks were the same drinks. The arithmetic was not wrong. The question was wrong.
What a real drink is worth in standard drinks
This is the table to screenshot. One US standard drink is 0.6 fl oz of pure ethanol, which is 14 grams, the definition the National Institute on Alcohol Abuse and Alcoholism uses. Everything below is that same measure applied to drinks people actually order.
| What you ordered | Size | ABV | Alcohol | Standard drinks |
|---|---|---|---|---|
| Regular beer | 12 fl oz | 5% | 14.0 g | 1.00 |
| Light beer | 12 fl oz | 4.2% | 11.8 g | 0.84 |
| Craft beer or IPA | 16 fl oz | 7% | 26.1 g | 1.87 |
| Hard seltzer | 12 fl oz | 5% | 14.0 g | 1.00 |
| Malt liquor, tall can | 24 fl oz | 8% | 44.8 g | 3.20 |
| Wine, standard pour | 5 fl oz | 12% | 14.0 g | 1.00 |
| Restaurant or heavy wine pour | 8 fl oz | 13.5% | 25.2 g | 1.80 |
| Champagne or prosecco | 5 fl oz | 12% | 14.0 g | 1.00 |
| Single shot | 1.5 fl oz | 40% | 14.0 g | 1.00 |
| Double shot | 3 fl oz | 40% | 28.0 g | 2.00 |
| Mixed drink or cocktail | 2.5 fl oz of spirits | 40% | 23.3 g | 1.67 |
| Strong or long-pour cocktail | 4 fl oz of spirits | 40% | 37.3 g | 2.67 |
Two things fall out of that table. First, a tall can of malt liquor on its own is more alcohol than three standard drinks, so one can and a driving decision is already a bad pairing. Second, the shape of a glass tells you nothing. A 5 oz wine pour and a 1.5 oz shot look nothing alike and are the same drink.
Your peak is later than you think
Alcohol does not appear in your blood the moment it goes down. It has to leave your stomach, cross the wall of your small intestine, and get picked up by the blood on the other side. On an empty stomach that is fast: research on absorption kinetics puts 99% of it across in about 45 minutes. After a real meal it can take 2 hours. In practice, blood alcohol peaks somewhere around 30 to 90 minutes after your last drink, and later if you ate.
That gap is the second big way people underestimate themselves. You finish the last round, you feel about how you felt twenty minutes ago, you decide that is your level, and then your level keeps climbing for another hour in the car park. This calculator asks how long ago your last drink was for exactly this reason. If the answer is under 90 minutes, it tells you plainly that the number it is showing you is where you are heading rather than where you are, and it pushes every one of its timing estimates back to allow for the climb still to come.
Sleeping it off takes longer than almost anyone expects
Nothing speeds up elimination. Not coffee, not a cold shower, not a big breakfast, not throwing up, not a run. Your liver works through alcohol at a roughly fixed rate whatever else you do, and that rate is about 0.015% of BAC per hour, give or take, which is the slowest process anybody applies impatience to.
So do the arithmetic on a normal heavy night. You stop drinking at 2 am and you are at 0.16%, which takes about six standard drinks in a couple of hours for an average-sized man. By 7 am you have burned off somewhere between 0.060% and 0.100%, so you are somewhere between 0.060% and 0.100%. At the slow end of the range you are still over the 0.08% limit at breakfast. At every point in the range you are over the 0.05% limit that applies in Utah and across most of Europe. Morning-after driving is not a technicality. It is one of the most common ways ordinary people get a DUI, and they are genuinely surprised, because they slept.
What this calculator cannot know
A short and honest list, because a page like this earns its keep by drawing its own boundaries.
It does not know your body composition. The r range is population statistics. Muscle carries water and fat does not, so two people of identical weight and sex can sit at opposite ends of it. It does not know what you ate. Food slows absorption and can lower your peak, sometimes considerably, but it changes when the alcohol arrives, not how much of it there is. It does not know your medications. A number of common ones amplify alcohol or interfere with clearing it, and some make a modest BAC dangerous on its own terms. It does not know your health. Liver disease, diabetes and other conditions change these numbers in ways no formula can guess. It does not know your tolerance. Tolerance changes how drunk you feel, not how much alcohol is in your blood, which is precisely why experienced drinkers are so often the ones caught out: they feel fine at a BAC that is illegal.
And one more that almost no calculator says out loud. The formula's split between men and women is a proxy for average body water, taken from studies that recorded sex assigned at birth, and validated equations for trans and non-binary people have not been published. That is a real limitation of the science and not a judgment about anybody. If you are unsure which option applies to you, pick the one that produces the higher estimate, which is the female setting. On this page, when in doubt, take the bigger number.
What the numbers mean, and where the lines are
In most US states the limit is 0.08% for drivers 21 and over. Utah uses 0.05%, as do most countries in Europe and much of the rest of the world. Commercial drivers are typically held to 0.04%, and drivers under 21 face zero tolerance limits of 0.00 to 0.02%. But the legal line is not where the trouble starts: measurable loss of judgment, divided attention and reaction time shows up from around 0.02%, well below any limit anyone can be arrested for, and it is worst in exactly the ways that matter behind a wheel. A limit is a line the state will punish you for crossing, not a line below which driving is fine.
At the other end, high blood alcohol is a medical problem rather than a legal one. If someone is confused or cannot be woken, is vomiting while sedated, is breathing slowly or irregularly, or has cold or bluish skin, that is alcohol poisoning, and it is a 911 call rather than a let-them-sleep-it-off. People die of this while their friends assume they are just very drunk.
Which brings us back to the only sentence on this page that is not an estimate. This calculator gives you a range built out of population averages, and the true figure for you personally can sit outside it. Only a calibrated breath or blood test measures your actual BAC. No calculator, this one included, can tell you that you are fit to drive, and this one will never try. If you have been drinking, the number to drive on is zero.