Blood Alcohol Content Calculator (Widmark Formula)
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 9/5/2026
Blood alcohol content is estimated with the Widmark formula: mass of pure alcohol ÷ (body weight × distribution coefficient), followed by a decline of about 0.15 g/L per hour. This estimate should never be used to decide whether to drive.
Explanation
The Widmark formula, developed in the 1930s and still used today as a reference in forensic toxicology, estimates the theoretical blood alcohol content from the amount of pure alcohol consumed, spread through the body's distribution volume (approximated by body weight multiplied by a coefficient r). This coefficient differs between men (0.68) and women (0.55), because the female body contains on average a lower proportion of body water: at equal consumption and weight, alcohol is therefore diluted in a smaller relative volume, producing a higher blood alcohol content. Once the theoretical peak is reached (generally 15 to 30 minutes after consumption, later if the meal was substantial), the body eliminates alcohol at a relatively constant rate of about 0.15 gram per liter of blood per hour, which allows the time needed to return to zero to be estimated. This formula remains an average estimate built from population data, not a precise individual measurement: many factors significantly change the actual result (having eaten or not, drinking speed, fatigue, medication use, each person's own metabolism), with gaps that can reach several tenths of a gram per liter compared to this theoretical estimate. Alcohol also has a measurable short-term effect on heart rate — see our resting heart rate calculator for a related indicator.
Example: a bottle of wine (75 cl, 12°), a 75 kg man, 3 hours elapsed
Inputs
Volume: 75 cl. Strength: 12%. Weight: 75 kg. Sex: male. Time elapsed: 3 hours.
Calculation
Mass of pure alcohol = 75 × 12 × 0.08 = 72 g. Peak blood alcohol content = 72 ÷ (75 × 0.68) ≈ 1.41 g/L. After 3 hours: 1.41 − (0.15 × 3) ≈ 0.96 g/L.
Result
The estimated blood alcohol content after 3 hours is about 0.96 g/L — still well above the legal driving limit (0.5 g/L in France, 0.08% BAC in most US states).
Frequently asked questions
Can this calculator tell me if I am fit to drive?
No, never. This is an average estimate built from population data, with a significant real individual margin of error: it never replaces a direct breathalyzer measurement, the only reliable way to make a driving decision. In France, the legal limit is 0.5 g/L of blood (0.2 g/L for novice drivers); in the United States it is typically 0.08% BAC. When in doubt, the only safe decision is not to drive and to find another way home.
Why does the distribution coefficient differ between men and women?
Because the female body contains on average a lower proportion of body water than the male body, at equal weight (more fat mass, which retains less alcohol than water-rich tissue). Alcohol consumed is therefore diluted in a smaller relative volume in a woman, producing a higher blood alcohol content at equal consumption and weight.
Why can the result differ so much from how I feel or from a real breathalyzer?
Because this formula does not account for many individual factors that genuinely influence alcohol absorption and elimination: eating before or during drinking noticeably slows absorption, the speed at which drinks are consumed influences the actual peak reached, and metabolism varies significantly from person to person. Subjective feelings of intoxication are also an unreliable indicator, often out of step with the actual level.
Does alcohol have other cardiovascular effects worth watching?
Yes: beyond its immediate effect on the nervous system measured here, regular alcohol consumption has a direct, measurable impact on blood pressure. If you track yours, our blood pressure calculator lets you compare a reading against the usual benchmarks.