BAC Calculator
This BAC calculator estimates your blood alcohol content from what you drank, your weight and sex, and when you drank it, using the Widmark formula. It goes further than a single number: enter each drink and its timing and you'll see your estimated BAC now, a curve over time, and a rough idea of how many hours until you'd be under the limit and back to zero.
Safety first: this is a rough estimate, not a breathalyzer. Impairment starts with the first drink, and no tool can tell you it's safe to drive. If you've been drinking, plan a ride, a taxi, or a sober driver. The only safe BAC for driving is zero.
Last updated July 15, 2026 Estimate only, not medical or legal advice
1 standard drink = a 12 oz beer (5%), a 5 oz glass of wine (12%), or a 1.5 oz shot (40%). Cocktails often count as 2 or more.
Never drive after drinking. This estimate can be wrong in either direction. Plan a ride home.
What is BAC and how is it estimated?
Blood alcohol content is the percentage of alcohol in your bloodstream. A BAC of 0.08% means 0.08 grams of alcohol per 100 millilitres of blood, which is the legal driving limit in every US state. The Widmark formula estimates it from the alcohol you drank, spread through the water in your body, minus what your liver has already cleared. It's a useful model, but only a breath or blood test measures the real number, and impairment can be present at any BAC above zero.
How your body clears alcohol
Your liver processes alcohol at a roughly steady pace, about one standard drink an hour, which lowers BAC by around 0.015% each hour. Nothing speeds this up in any meaningful way: coffee makes you a wide-awake drunk, not a sober one, and water, food, and cold showers don't clear alcohol from your blood. The table shows why patience is the only real option, since a night out can keep you over the limit well into the next morning.
| Peak BAC | Hours to under 0.08 | Hours to zero |
|---|---|---|
| 0.10% | ~1.3 hr | ~6.7 hr |
| 0.15% | ~4.7 hr | ~10 hr |
| 0.20% | ~8 hr | ~13.3 hr |
| 0.25% | ~11.3 hr | ~16.7 hr |
Frequently asked questions
Most calculators use the Widmark formula. It estimates BAC from the grams of alcohol you drank, your body weight, and a sex-based distribution factor, then subtracts the alcohol your body has already processed. Roughly, more alcohol and less body weight raise BAC, and time lowers it at about 0.015% per hour. This is an estimate only, because real BAC depends on food, metabolism, medications, and other factors a formula can't see.
Your body clears alcohol at a fairly steady rate, about 0.015% BAC per hour, and nothing reliably speeds it up. Not coffee, not a cold shower, not water. So a BAC of 0.08 takes roughly five to six hours to reach zero, and there's no shortcut. The calculator shows an estimated time to fall under 0.08 and to reach zero, but treat both as rough, and never assume you're safe to drive just because a tool says so.
In every US state the limit for drivers 21 and over is 0.08%, and it's lower, 0.04%, for commercial drivers. Many states have zero-tolerance laws under 0.02% for drivers under 21. Utah's limit is 0.05%. Impairment, though, begins well before any limit: judgment, reaction time, and coordination are affected from the very first drink, which is why the safest BAC for driving is zero.
No. It gives a rough estimate, not a measurement, and it can be off in either direction. The only safe amount of alcohol before driving is none. If you have been drinking, plan another way home: a ride, a taxi, public transit, or a sober driver. Use this tool to understand how long alcohol lingers, not to decide whether to get behind the wheel.
Yes. A smaller person reaches a higher BAC from the same drinks because there's less body water to dilute the alcohol. Sex matters for a similar reason: on average women have a lower proportion of body water than men of the same weight, so the same drinks tend to produce a higher BAC. The formula uses a distribution factor of about 0.68 for men and 0.55 for women to reflect this average difference.
In the United States a standard drink contains about 14 grams of pure alcohol. That's roughly a 12-ounce beer at 5%, a 5-ounce glass of wine at 12%, or a 1.5-ounce shot of 80-proof spirits at 40%. Cocktails and craft beers often contain more than one standard drink, so count generously. Enter the number of standard drinks and when you had them for the closest estimate.
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