Alcohol Calculator (BAC)

This calculator estimates Blood Alcohol Content (BAC) using the Widmark formula, based on your weight, gender, number of standard drinks, and time elapsed since your first drink. BAC is the percentage of alcohol in your bloodstream, and it's the same underlying measurement law enforcement uses with a breathalyzer or blood test, though this tool only produces an estimate rather than a certified reading.

The formula behind this calculator dates back to work by Swedish physician Erik Widmark in the 1930s, who studied how alcohol distributes through body water and how quickly the liver clears it. Nearly a century later, the same basic approach — alcohol consumed, diluted across estimated body water, minus a steady elimination rate over time — is still the standard starting point taught in toxicology and used informally for alcohol education, even though real BAC depends on more variables than any formula can fully capture.

Because alcohol affects more than just blood chemistry, it's worth looking at related effects too — see the Sleep Cycle Calculator if you're curious how a night of drinking might affect your sleep timing, or the Water Intake Calculator for a baseline on daily hydration, since alcohol is a diuretic that increases fluid loss.

The Widmark formula estimates how much alcohol is distributed through your body water (approximated from body weight and a gender-based constant), then subtracts an average elimination rate of about 0.015% BAC per hour to account for alcohol your liver has already metabolized since you started drinking.

That 0.015%-per-hour figure is a population average, not a personal constant — actual elimination rate varies with liver function, medication use, tolerance built up from regular drinking, and even genetic differences in how efficiently someone's body breaks down alcohol. The formula also assumes drinks were spread evenly over the stated time period; a genuinely realistic BAC curve rises quickly while actively drinking and only falls afterward, so this estimate is closer to an average than a moment-by-moment reading.

Your estimated BAC places you in a range from Minimal effects up to Severe impairment. This is a rough estimate only — actual BAC and impairment can be higher or lower than calculated depending on individual factors, and no BAC level is safe for driving.

Roughly: Minimal (under 0.03%) suggests little noticeable effect for most adults; Mild (0.03-0.06%) brings light relaxation and slightly reduced inhibition; Reduced Coordination (0.06-0.10%) is where motor skills and judgment start noticeably declining; Significant Impairment (0.10-0.20%) involves clear coordination and reaction-time problems; and Severe (0.20% and above) carries real medical risk, including possible loss of coordination, confusion, or worse. These bands are general reference points, not a precise measure of how impaired any individual actually is at a given estimated BAC.