Estimate blood alcohol concentration using the Widmark formula.
Widmark formula: BAC (g/L) = (alcohol_g / (weight_kg × r)) − β × hours, with r = 0.68 (men) or 0.55 (women) and β ≈ 0.15 g/L per hour. Estimate only — never use this calculator to decide whether to drive.
Blood alcohol concentration (BAC) is the biological correlate of intoxication. Most jurisdictions set a legal driving threshold — 0.5 g/L in France and most EU countries, 0.8 g/L in the US and UK, 0.2 g/L for novice drivers in many places. The threshold matters because impairment is non-linear: at 0.5 g/L, reaction time slows by ~30 %, peripheral vision narrows, and risk of accident roughly doubles vs sober. People underestimate their BAC because they count drinks instead of grams of ethanol, and because they ignore body composition and elimination rate. A "couple of beers" can easily put a small woman over the legal limit while leaving a large man at half of it. The Widmark formula gives a first-order estimate from drink composition, body weight and time elapsed — useful for self-awareness and planning, not for legal certification.
Pure ethanol consumed (grams): drinks_count × volume_per_drink_mL × ABV_fraction × 0.789 (ethanol density, g/mL).
Peak BAC (g/L) = ethanol_g / (body_weight_kg × r), where r is the Widmark coefficient: 0.68 for men, 0.55 for women. r reflects total body water as a fraction of body mass — men carry more water (so dilute more), women carry more fat (which is alcohol-impervious).
BAC at time t = max(0, peak − β × t), where β ≈ 0.15 g/L per hour for an average drinker. β has individual variance: regular drinkers eliminate at 0.18–0.20 g/L/h; non-drinkers at 0.10–0.12 g/L/h; East Asian populations with ALDH2 deficiency at as low as 0.07 g/L/h.
Time to sober = peak / β — assumes no further drinking from t = 0.
Pick sex (changes r). Enter body weight (kg or lb). Enter the number of drinks, the volume per drink in mL, and the alcohol by volume (%). Pick the hours since the first drink (the calc assumes all drinks were consumed at t = 0 — a worst-case approximation for steady drinking; real BAC peaks 30–90 min after the last drink). The result shows peak BAC, current BAC, time to sober, and a BAC-decay curve with dashed reference lines at 0.5 and 0.8 g/L (typical legal thresholds).
Two beers (250 mL × 5 % ABV) for a 75 kg male, 1 hour ago.
A glass of wine (150 mL × 12.5 % ABV) for a 60 kg female, 30 min ago.
This calc is an estimate. Never use it to decide whether to drive. The Widmark formula has ±30 % individual variance even before accounting for medication interactions, food consumption, fatigue and acute illness. A breath analyzer is the only field-reliable tool. The legal authority's instrument trumps any calculator output.
Food slows absorption but does not reduce total BAC. Eating before drinking flattens the absorption curve so peak BAC arrives later and lower, but the area under the curve — total exposure — is the same. The calc assumes empty-stomach absorption.
Drinking spread out over hours. The calc treats all drinks as consumed at t = 0. If you drank 2 beers at hour 0 and 2 more at hour 2, your real BAC trajectory is two stacked Widmark curves, which is harder to math by hand. Approximation: take the average drinking time as t = 0 and use total drinks.
Sex isn't binary in pharmacokinetics. The 0.55 / 0.68 split is a population average. Trans individuals on hormone therapy and intersex people have intermediate r values; precise modeling requires body-composition data (DEXA scan).
Body composition matters more than weight. r reflects body water fraction. Two people of the same weight with very different body fat will have different r values. The calc uses sex as a proxy; high body fat under-water-dilutes alcohol → higher BAC.
Pregnancy, liver disease, certain medications dramatically change β (elimination rate). Antibiotic metronidazole, antifungal ketoconazole, and the diabetes drug metformin all interfere with alcohol metabolism. The calc does not account for any of this.
Alcohol absorption from cocktails is faster than beer. Carbonated mixers (vodka tonic) accelerate gastric emptying → faster absorption → higher peak. The calc treats drinks as biologically interchangeable on a per-gram-ethanol basis.
Standard drink size varies by country. UK "unit" = 8 g ethanol; US "standard drink" = 14 g; Japan "drink" = 19.75 g. The calc takes raw mL × ABV so units cancel out — but check that your inputs are correct (a US "drink" of beer is 12 oz = 354 mL, not 250).
Acute vs chronic tolerance. Heavy drinkers feel less impaired at the same BAC, but their reaction times are still impaired. The legal threshold is BAC, not perceived intoxication.