About BAC Levels

We are health researchers and developers who spent too long watching BAC calculators get the pharmacokinetics wrong in ways that matter.

The Widmark formula — published by Erik Widmark in 1932 and still the basis for every credible BAC estimate — requires accurate body water constants to produce useful output. Most tools online use the wrong constants, or apply the same constant regardless of sex, which produces errors of 15–20% in the estimate.

We use Widmark's original fixed constants — r = 0.68 for men, r = 0.55 for women — rather than a one-size-fits-all number. The female and male values are different because the physiology is different, and that difference is not cosmetic — it changes the output meaningfully. A height-and-age-adjusted version of this constant exists in the literature (Watson, 1981); we don't collect those inputs, so we use the population averages instead and explain that tradeoff plainly on our methodology page.

Beyond the formula, the other thing most tools ignore is time. BAC is not a static number. It peaks after absorption and declines at a rate that varies by body weight, food consumption, and how long ago the first drink was. We built the time curve into every calculation because a snapshot BAC at "right now" is less useful than understanding where the number is heading.

All legal BAC limits — federal guidance, per-state driving limits, and workplace standards — are sourced from official state statutes and NHTSA publications. We update them when state law changes.

No data leaves your browser. We have no server-side storage of any kind. The inputs you enter exist only in your session.

These tools are for informational and educational purposes. BAC estimates are approximations — individual metabolism varies, and no calculator replaces a breathalyzer or blood test. If you are making a decision about driving or safety, the only right answer is not to drink and drive, regardless of what any estimate shows.

Questions or data corrections: Contact us