Drunk Calculator: Blood Alcohol Calculator (BAC)

Use this to get a rough estimate of your blood alcohol content (BAC) based on how much you have had to drink, your body weight, and how much time has passed. It uses the Widmark formula, the standard equation most BAC calculators are built on.

Estimate your BAC

How this calculator works

The Widmark formula estimates blood alcohol content from the grams of pure alcohol you have consumed, your body weight, a distribution constant based on average body composition, and an average elimination rate of about 0.015% per hour. It is the same basic method used by most consumer BAC calculators and educational tools, though none of them, including this one, can measure your actual BAC. Real BAC depends on food intake, drinking speed, medication, and individual metabolism, none of which a formula can account for.

Popular drinks

Pick a specific drink below for a version of this calculator pre-filled with its typical ABV, so you do not have to look it up yourself.

Frequently asked questions

Is this calculator accurate?

It gives a reasonable estimate using a well-established formula, but it cannot replace an actual breathalyzer or blood test. Treat the result as a rough guide, not a precise measurement.

Can I use this to decide if I am okay to drive?

No. This tool is for information only. If there is any doubt at all about whether you are okay to drive, do not drive.

Why does body weight matter so much?

Alcohol distributes through your body water, so a heavier person generally has more body water to dilute the same amount of alcohol into, which is why the same number of drinks produces a lower estimated BAC for someone who weighs more.

What counts as “a drink” anyway

A US standard drink is defined as 14 grams of pure alcohol, which works out to roughly 12 US fl oz (355 ml) of a 5% beer, 5 fl oz (148 ml) of 12% wine, or 1.5 fl oz (44 ml) of 40% spirits. Different countries define a standard drink differently (the UK unit, for example, is 8 grams of alcohol, not 14), which is one reason a “one drink an hour” rule of thumb does not translate cleanly across countries. This calculator works directly from your actual volume and ABV rather than a fixed unit, specifically to avoid that confusion.

Legal limits vary by country and by driver type

In most of the US, the legal driving limit is 0.08% BAC for drivers 21 and over, with lower limits (often 0.04% or 0.02%) for commercial drivers, and zero-tolerance policies for drivers under 21 in many states. Other countries set their limits lower still, several European countries use 0.05% or 0.02% as their general limit. None of that changes the advice here: if there is any doubt about whether you are under a limit, do not drive, regardless of what a calculator estimates.

Why the same person can get different results on different nights

Food intake is the single biggest real-world variable this formula cannot see. Drinking on an empty stomach lets alcohol absorb into your bloodstream much faster, producing a higher peak BAC even at the exact same number of drinks. Hydration, sleep, medication, and simple individual variation in liver enzyme activity all shift the real number too, sometimes by a noticeable margin. Treat the estimate here as a starting point for understanding roughly where you stand, not a substitute for paying attention to how you actually feel.

Frequently asked follow-ups

Does eating before drinking really change my BAC?

Yes, meaningfully. Food slows the rate alcohol moves from your stomach into your bloodstream, which lowers your peak BAC even though the total amount of alcohol consumed is unchanged.

Why do the drink-specific calculators on this site give slightly different results for the same number of drinks?

Because each drink has a different ABV and serving size pre-filled. A 5% seltzer and a 4.2% light lager both count as “one drink” colloquially, but they do not contain the same grams of alcohol, so they produce different BAC estimates for the same count.