Blood Alcohol Calculator

An educational estimate, using the same formula as forensic toxicology, and its real limits

This calculator uses the Widmark formula, created in 1932 and still the basis for BAC (blood alcohol concentration) estimates in forensic toxicology, alongside the Watson/Forrest variant, which swaps the fixed sex-based distribution factor for an individualized calculation based on estimated body water from your height and weight, more accurate for people whose body composition sits outside Widmark's average. You build a list of the drinks you had, each with type, volume, alcohol content, and time, and the tool sums each dose's contribution over time, shows the estimated peak, the decay curve, and the time your estimated BAC returns to zero. But it is important to understand the limits of this: the formula assumes complete, instant absorption and does not account for food in your stomach, medication, individual tolerance, sleep, hydration, or the hundreds of other factors that change the real result from person to person, sometimes by a lot. That is why this tool is educational only, never a measurement, and should never guide the decision to drive.

From your profile to the night's drinks, in a few fields

1. Enter your sex, age, height, and weight, and pick a calculation method (fixed Widmark or individualized Watson/Forrest).
2. Add each drink you had with its type, volume, alcohol content, and approximate time, adjusting the elimination rate if you want.
3. See the estimated BAC right now, the peak, the decay curve, the estimated time back to zero, and how it compares to Brazil's legal limits, always with the warning that this does not decide whether you can drive.

Use this tool on your site

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Sources and references for this tool

These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.

• Codigo de Transito Brasileiro, Lei 9.503/1997 (compilado)Presidencia da Republica, Official text of articles 165 (administrative infraction) and 306 (traffic crime) on driving under the influence.
• Resolucao CONTRAN 432/2013Ministerio dos Transportes e CONTRAN, Sets the breathalyzer tolerance margin and the reference-value table applied to the measured result.
• Efeitos do alcool no organismoNational Institute on Alcohol Abuse and Alcoholism, Reference on alcohol absorption, distribution and elimination, the basis for individual variation in the result.
• Direcao sob efeito de alcoolCenters for Disease Control and Prevention, International reference on the risks of alcohol-impaired driving, used for the tool warning.

Frequently asked questions

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