Blood Alcohol Calculator
Estimate your blood alcohol level by entering your weight, drinks consumed, and time elapsed.
Estimate your Blood Alcohol Concentration (BAC) percentage and sobriety time using the standard Widmark formula. This tool assumes 14g of pure alcohol per standard drink and is strictly for educational purposes, not for determining safety to drive.
A blood alcohol calculator can only ever produce an estimate — it has no way to account for your actual metabolism, what you ate, or how your body individually processes alcohol. What it can do is show roughly how weight, sex, time, and drink count interact to produce a blood alcohol concentration number, which is useful for understanding the math even though no number from a calculator should ever be the basis for deciding whether it’s safe to drive.
How to calculate alcohol blood level: the Widmark formula
The standard method, developed by Swedish researcher Erik Widmark in the 1930s and still used in forensic and legal contexts today, is:
BAC (%) = (Alcohol consumed in oz × 5.14 ÷ Body weight in lbs × r) − (0.015 × Hours since first drink)
“r” is the distribution ratio — how much of the body is water that alcohol can dissolve into — and it’s the variable that splits the formula by sex. The 5.14 figure converts ounces of alcohol into a percentage relative to body weight; the 0.015 represents the average rate the body eliminates alcohol per hour, which keeps running from the moment drinking starts, not just after it stops.
Why men and women get a different blood alcohol percentage from identical drinks
The distribution ratio (r) commonly used is 0.68 for men and 0.55 for women, though individual sources put it anywhere from 0.68–0.73 for men and 0.55–0.66 for women, since actual body composition varies person to person. The underlying reason is body water content: men average around 58% body water, women around 49%, and alcohol dissolves into that water, not into fat or bone.
Practically, this means two people of identical weight who drink the same amount can land on noticeably different blood alcohol levels if one is male and one is female — it isn’t a rounding error in the formula, it’s a real physiological difference the formula is built to capture.
What actually counts as “one drink” in the formula
The “alcohol consumed” variable isn’t drink count — it’s the actual volume of pure ethanol, which differs by beverage:
| Beverage | Typical serving | Pure alcohol |
|---|---|---|
| Beer (5% ABV) | 12 oz | 0.6 oz |
| Wine (12% ABV) | 5 oz | 0.6 oz |
| Spirits (40% ABV) | 1.5 oz shot | 0.6 oz |
These three are designed to all contain roughly the same amount of pure alcohol — which is the entire point of a “standard drink.” A double pour, a craft beer at 8% ABV, or a generously poured glass of wine all break that assumption and push more actual alcohol into the calculation than a casual drink count would suggest.
How fast blood alcohol concentration actually drops
The body eliminates alcohol at a fairly fixed average of 0.015% per hour, and almost nothing meaningfully speeds that up. Coffee, cold showers, and food don’t accelerate elimination — food slows how fast alcohol gets absorbed into the bloodstream in the first place, which is a different mechanism entirely, and it has no effect once the alcohol is already there.
This is also why “I’ll just wait it out” math gets people in trouble: at 0.015% per hour, dropping from 0.10% to under the 0.08% legal limit takes well over an hour, and someone who started higher than that needs considerably longer than they usually assume.
Legal blood alcohol concentration limits
| Driver category | Limit |
|---|---|
| Standard limit (most US states) | 0.08% |
| Utah | 0.05% |
| Commercial (CDL) drivers | 0.04% |
| Under-21 drivers (zero tolerance) | 0.00–0.02% |
| Most of the EU, Australia | 0.05% |
| Japan, India | 0.03% |
NHTSA crash data puts a driver at 0.08% at roughly four times the fatal crash risk of a sober driver — which is worth sitting with, since the legal threshold isn’t where impairment starts, it’s just where the law draws a line. Measurable impairment in reaction time and judgment begins well below 0.08%.
What different blood alcohol levels actually feel like
| BAC range | Typical effects |
|---|---|
| 0.01–0.05% | Relaxation, reduced alertness, mild judgment impairment |
| 0.06–0.15% | Slurred speech, reduced coordination, impaired judgment and balance |
| 0.16–0.30% | Difficulty walking and speaking, confusion, nausea, possible memory gaps |
| 0.31%+ | Risk of vomiting, loss of consciousness; medically dangerous territory |
The disconnect between how impaired someone feels and how impaired they actually are tends to widen as the number climbs — most people at 0.08% genuinely believe they’re functioning closer to normal than they are, which is exactly the gap a number on a screen can correct that self-assessment can’t.
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BAC drops at approximately 0.015% per hour as the liver metabolizes alcohol. A person with a peak BAC of 0.15% will take roughly 10 hours to fully sober up. Nothing speeds this process — coffee, water, and food only affect how you feel, not how quickly your liver clears alcohol.
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Women reach higher BAC levels than men of equal weight for two reasons: a lower body water percentage (alcohol distributes through water, not fat) and lower average activity of alcohol dehydrogenase, an enzyme involved in alcohol metabolism. The Widmark formula accounts for this with different distribution factors — 0.73 for males and 0.66 for females.
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In the United States, Canada, and the United Kingdom (England and Wales), the legal limit is 0.08% BAC. Australia, Germany, France, and most of Europe use 0.05%. Japan sets the limit at 0.03%, while Sweden and Norway use 0.02%. Commercial and new drivers face stricter limits in nearly every country.
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Food slows the rate of alcohol absorption into the bloodstream, which delays the peak BAC and reduces how quickly you feel impaired. However, eating does not significantly reduce the total BAC you ultimately reach — it mostly spreads the absorption curve over a longer period. Drinking on an empty stomach produces a faster, higher BAC peak compared to drinking after a meal.