BAC Calculator

This calculator provides a rough, formula-based estimate of blood alcohol content from body weight, sex, number of drinks, and time elapsed. Before anything else: it cannot tell you whether you’re safe to drive, and it should never be used to make that decision. If you’ve been drinking, the only safe choice is not to drive — arrange a ride, use a taxi or rideshare, or stay where you are.

How the BAC Calculator Works

Enter your sex, body weight, number of standard drinks consumed, and hours since your first drink, and the calculator applies the Widmark formula — a long-standing method for estimating BAC based on alcohol consumed, body weight, a sex-based water distribution factor, and an average alcohol elimination rate over time. The result includes an estimated BAC percentage and how many hours until it’s estimated to reach zero.

Why This Estimate Cannot Tell You Whether You’re Safe to Drive

This needs to be stated as plainly as possible: this calculator, like any BAC estimation formula, produces a rough population-average approximation — not a measurement of your actual, individual blood alcohol level at this moment. Real BAC is affected by far more than the four inputs this calculator asks for: how quickly you drank, whether you ate food and how much, individual differences in metabolism and liver function, medications, hydration, and simple biological variation between people of the same weight and sex. Two people with identical inputs into this calculator can have genuinely different actual BAC levels. Impairment itself also doesn’t wait for a specific number — judgment, reaction time, and coordination can all be affected below commonly cited legal limits, and “estimated to be under the limit” is not the same as “safe to drive.” The only reliable way to know you’re safe to drive after drinking is not to drink and then drive at all.

What a “Standard Drink” Actually Means — and Why It’s Easy to Underestimate

This calculator’s “number of drinks” input assumes standard drink sizes — roughly 14 grams of pure alcohol per drink, which corresponds to about 12 ounces of regular beer, 5 ounces of wine, or 1.5 ounces of distilled spirits. Real-world servings frequently exceed these standard sizes considerably: a mixed drink poured at home, a pint of craft beer with higher-than-average alcohol content, or a generous restaurant pour can each represent well more than one standard drink, even though it’s consumed as a single serving. Underestimating how many standard drinks you’ve actually consumed is one of the most common ways any BAC estimate — including this one — ends up significantly understating actual alcohol level.

Why Time Matters, But Elimination Rate Varies Between People

This calculator assumes a fixed average rate at which the body eliminates alcohol over time (roughly 0.015% BAC per hour), but actual elimination rate varies between individuals based on liver function, overall health, and other factors — meaning the “hours until zero” figure this calculator provides is, like the BAC estimate itself, an approximation rather than a guarantee specific to your body. There is no reliable way to speed up alcohol elimination through coffee, cold showers, exercise, or any other commonly suggested method — time is the only factor that actually reduces BAC, and even that timeline varies by individual in ways this or any general calculator can’t precisely capture.

If You Need a Safe Ride Home

Planning transportation before drinking begins is the most reliable way to avoid ever facing this decision under the influence of alcohol, when judgment about one’s own impairment is itself compromised. Designating a sober driver in advance, arranging a rideshare or taxi ahead of time, or simply planning to stay overnight where you are are all far more reliable safety measures than any BAC estimate, from this calculator or any other source.

Calorie Content of Alcoholic Drinks

If you’re tracking alcohol consumption for reasons unrelated to driving safety — general calorie awareness, for instance — the Calorie Calculator and related nutrition tools on this site can help account for alcohol’s caloric contribution alongside food intake, a separate and unrelated use case from BAC estimation.

Age-Related Calculations

If you need to confirm an exact current age for any reason related to this or another calculation, the Age Calculator handles that separate, unrelated calculation directly from a birth date.

Frequently Asked Questions

Can this calculator tell me if I’m safe to drive?

No — this or any BAC estimation tool should never be used to decide whether it’s safe to drive. It provides a rough, population-average approximation that doesn’t account for many individual factors affecting your actual alcohol level and impairment. If you’ve been drinking, don’t drive — arrange another way to get home.

Why might my actual BAC be higher than this calculator estimates?

Common reasons include underestimating drink sizes (many servings exceed the standard drink measurement this calculator assumes), drinking quickly rather than over a longer period, not having eaten food, and individual differences in metabolism that this general formula can’t account for.

Does coffee or a cold shower help sober up faster?

No — neither actually reduces blood alcohol content. Only time allows the body to metabolize and eliminate alcohol, and even that elimination rate varies between individuals in ways a general calculator can’t precisely capture.

What counts as a standard drink?

Roughly 14 grams of pure alcohol — approximately 12 ounces of regular beer, 5 ounces of wine, or 1.5 ounces of distilled spirits. Many real-world servings, particularly mixed drinks or higher-alcohol beers, contain meaningfully more than one standard drink even when served as a single serving.

What should I do instead of checking a BAC calculator before driving?

Plan transportation before drinking begins — a designated sober driver, a rideshare or taxi arranged in advance, or simply staying where you are overnight. Deciding whether you’re safe to drive after drinking is a judgment alcohol itself impairs, which is exactly why the decision is safest made in advance, not estimated afterward.