Calculadora de Teor de Álcool no Sangue (BAC)

The blood alcohol concentration (BAC) calculator estimates the percentage of alcohol in the bloodstream after a given number of standard drinks, using body weight, sex, and time elapsed. It is built on the Widmark formula, a century-old estimation method. The result is an estimate for general reference only. It is not accurate enough, and this tool is not intended, to be used to decide whether it is safe to drive, operate machinery, or care for someone else.

A fórmula

BAC = (alcohol consumed in grams / (body weight in grams x distribution ratio r)) - (elimination rate x hours since first drink)

• alcohol consumed (g) = number of standard drinks x grams of pure alcohol per standard drink
• distribution ratio r = an estimate of how alcohol distributes through body water and tissue, commonly given as approximately 0.68 for men and approximately 0.55 for women, though individual values vary
• elimination rate = the average rate the body clears alcohol, commonly approximated at about 0.015 percent BAC per hour, though this also varies between individuals

Widmark formula, developed by Erik Widmark in the 1930s

How the calculation works

The Widmark formula estimates BAC by dividing the total grams of alcohol consumed by an estimate of the body water and tissue available to distribute it in, then subtracting the amount the liver has already metabolized based on time elapsed. Body weight and an average distribution ratio stand in for actual body water content, which is why the formula uses commonly cited average ratios rather than measuring individual body composition.

A standard drink is defined by the U.S. National Institute on Alcohol Abuse and Alcoholism (NIAAA) as containing about 14 grams of pure alcohol, roughly the amount in a 12-ounce regular beer, a 5-ounce glass of wine, or a 1.5-ounce shot of distilled spirits, though actual alcohol content varies by beverage strength and pour size.

The elimination term subtracts a fixed rate per hour from the peak estimate, reflecting the fact that the liver metabolizes alcohol at a roughly steady rate over time rather than at a rate proportional to how much is in the bloodstream.

How to read your result

BAC is expressed as a percentage of alcohol in the blood. The table below gives commonly cited, generalized associations between BAC and observable effects; individual responses vary considerably and should never be relied on to judge one's own impairment.

Legal limits and why they vary

The legal BAC limit for driving is set by national or, in some countries, regional law, and it is not the same everywhere. Many jurisdictions set it at 0.08 percent, but others set it lower, including 0.05 percent or lower in a large number of countries, and some apply a near-zero limit for new or commercial drivers. This calculator does not state a single legal limit because none applies universally; check the specific limit that applies in the relevant jurisdiction before making any legal or safety judgment.

Impairment in reaction time, judgment, and coordination begins well below common legal limits and below the level most people would identify as feeling drunk. Legal limits describe where a jurisdiction has drawn an enforcement line, not the point below which driving or other safety-critical activity becomes risk-free.

Absorption and elimination over time, and why BAC keeps rising after the last drink

Alcohol must be absorbed from the stomach and small intestine into the bloodstream before it registers as BAC at all, and that absorption is not instantaneous. On an empty stomach, absorption is fast and BAC can peak within about 30 minutes of the last drink; with food in the stomach, especially fatty food, absorption slows and peak BAC can be delayed by an hour or more. Someone who stops drinking can still see their BAC climb for a while afterward, because alcohol already swallowed is still being absorbed even though no more is being consumed.

Once absorption is essentially complete, the elimination term in the Widmark formula takes over, clearing alcohol at a roughly constant rate, commonly approximated at about 0.015 percent BAC per hour, regardless of how high the peak was. This near-linear clearance means a very high BAC does not come down proportionally faster than a moderate one; it simply takes a correspondingly longer stretch of time to reach zero.

A calculation performed too soon after the last drink therefore tends to understate what BAC will shortly become, and is not a safe substitute for an actual measurement.

Limitações

• This is a population-average estimate, not a measurement. Actual BAC depends on factors this calculator cannot fully account for, including food intake, drinking speed, medications, liver function, hydration, and individual metabolism, and can differ substantially from the estimated figure in either direction.
• It must never be used to decide whether it is safe to drive, operate machinery, or perform any other safety-critical task. The only reliable way to confirm BAC is a breath, blood, or urine test administered by a qualified professional or a certified device; if there is any doubt, do not drive.
• Legal BAC limits vary by country and even by region within some countries, and by driver category, including lower limits for new or commercial drivers. This tool does not display a single legal limit because no single figure applies everywhere.
• It is not validated for people with liver disease, for pregnant individuals, for adolescents, or for anyone with unusually high alcohol tolerance, all of which can change how alcohol is metabolized or how impairment presents relative to a calculated BAC.
• BAC can continue rising for up to an hour or more after the last drink while absorption finishes, so a calculation performed shortly after drinking stops will understate the true peak; never treat a low or moderate estimate taken right after drinking as evidence that it is safe to drive.
• Feeling sober, or having developed a tolerance to alcohol's subjective effects, does not mean coordination, reaction time, and judgment are unimpaired at a given BAC; tolerance changes how impairment feels, not how much actual risk it carries.
• If someone shows signs of alcohol poisoning, including confusion, vomiting, slow or irregular breathing, seizures, pale or bluish skin, or unresponsiveness, treat it as a medical emergency and contact emergency services immediately rather than estimating BAC.

Perguntas frequentes

Is this calculator accurate enough to tell me if I can drive?

No. It provides a rough estimate for general reference only. Actual BAC depends on many individual factors this calculator cannot measure, and the only reliable way to know your BAC is a certified breath or blood test. If there is any doubt, do not drive.

What counts as one standard drink?

In the United States, NIAAA defines a standard drink as about 14 grams of pure alcohol, roughly a 12-ounce regular beer, a 5-ounce glass of wine, or a 1.5-ounce shot of distilled spirits. Stronger beers, wines, or cocktails contain more alcohol per serving than this reference amount.

Why does the calculator ask for sex or a distribution ratio?

The Widmark formula uses an average distribution ratio that differs by sex because body water content, which alcohol distributes into, tends to differ between average male and female bodies. It is a population average and does not reflect any individual's actual body composition.

Does the legal driving limit differ by country?

Yes, substantially. Some countries use 0.08 percent, many use 0.05 percent or lower, and some apply a near-zero limit for new or commercial drivers. Always check the specific legal limit for the jurisdiction in question rather than assuming one figure applies everywhere.

Why does BAC keep rising after I stop drinking?

Alcohol already swallowed still has to be absorbed from the stomach and intestine into the bloodstream, which takes time, especially with food present. BAC can keep climbing for roughly 30 minutes to an hour or more after the last drink as that absorption finishes, even though no more alcohol is being consumed.

Referências

1. National Institute on Alcohol Abuse and Alcoholism. What Is A Standard Drink?
2. National Institute on Alcohol Abuse and Alcoholism. Alcohol's Effects on Health.
3. CDC. Alcohol Use.