Blood Alcohol Concentration: Widmark formula

The BAC calculator estimates Blood Alcohol Concentration in grams per liter (g/L) using the Widmark formula (Erik M.P. Widmark, Lund University Sweden 1932): BAC = (alcohol_g / (weight_kg × r)) − β × t, where:

1. alcohol_g is pure ethanol consumed in grams (1 ml ethanol = 0.789 g)
2. weight_kg is body weight
3. r is the Widmark factor = body water distribution volume: r = 0.68 male, r = 0.55 female (Watson 1981 J Stud Alcohol 42:547-56 with TBW more accurate)
4. β is the elimination rate = 0.15 g/L/hour (range 0.10-0.20 individual, depends on liver ADH alcohol dehydrogenase)
5. t is time elapsed since ingestion in hours.

Example: 75 kg man drinks 2 beers 33 cl 5% (33×0.05×0.789 = 13 g alcohol/beer × 2 = 26 g) after 1 hour: BAC = (26 / (75×0.68)) − 0.15×1 = 0.510 − 0.15 = 0.36 g/L. Italy uses g/L (legal limit 0.5); USA uses % w/v (limit 0.08% = 0.8 g/L).

Ethanol (CH₃CH₂OH) density 0.789 g/ml at 20°C: 1 ml = 0.789 g. An Italian standard drink unit (UA) per Italian Health Ministry "Healthy eating guidelines 2018" CREA = 12 g pure alcohol = 1 beer 33 cl 5% (13 g) = 1 wine glass 125 ml 12% (12 g) = 1 spirit 40 ml 40% (13 g). WHO 2018 + LARN SINU 2014 + Italian Health Ministry: men 2-3 UA/day, women 1-2 UA/day, over-65 max 1 UA/day, 0 in pregnancy/lactation, 0 minors <18 (Italian L. 189/2012 alcohol sale to <18 forbidden). NHTSA USA classifies BAC: 0.02 g/L relaxation; 0.05 coordination decline (EU/Italy adult limit); 0.08 marked impairment (USA limit); 0.15 slurred speech; 0.30 alcoholic stupor; 0.40 coma; >0.50 death risk. Women show higher BAC at equal alcohol+weight due to: 1) lower TBW Total Body Water 50% vs 60% male; 2) lower gastric ADH activity (Frezza-Lieber 1990 NEJM 322:95); 3) luteal phase reduced clearance (Sutker 1987).

Italian Road Code art. 186: limits and penalties

The Italian Road Code (Codice della Strada D.Lgs. 30/4/1992 n. 285 as amended L. 120/2010 + L. 41/2016 vehicular homicide) at art. 186 "Driving under alcohol influence" establishes 3 progressive thresholds:

• BAC 0.5-0.8 g/L administrative offense: fine 544-2,174 € + license suspension 3-6 months + 10 points deduction
• BAC 0.8-1.5 g/L criminal offense: arrest up to 6 months + fine 800-3,200 € + suspension 6m-1y
• BAC >1.5 g/L serious crime: arrest 6m-1y + fine 1,500-6,000 € + suspension 1-2y + vehicle confiscation if driver-owned + 10 points. Novice drivers (3y from license), professional drivers (taxi, NCC, freight, hazmat), under-21: 0.0 g/L zero tolerance (art. 186 bis L. 120/2010): 0-0.5 fine 168-672 €; above multiplied +1/3. Refusing breathalyzer: maximum penalty as >1.5 g/L bracket. Vehicular homicide BAC >1.5: prison 8-12 years (L. 41/2016 codice penale art. 589 bis); 0.8-1.5 prison 5-10 years

Italian standard drink table (UA)

(Source: Italian Health Ministry healthy eating guidelines 2018 + ISS Higher Health Institute National Alcohol Observatory www.epicentro.iss.it; 1 UA = 12 g pure alcohol).

Alcohol elimination time table

Elimination rate averages β = 0.15 g/L/hour (Widmark 1932), individual range 0.10-0.20 g/L/h. Modulating factors:

• Genetics ADH/ALDH: ADH1B*2 variant (Asia 70%, Europe 5%) eliminates 40% faster; ALDH2*2 deficiency (40% Asians flush response) accumulates toxic acetaldehyde
• Age: elderly metabolize −20% vs young (Vestal 1977)
• Sex: women 0.12-0.13 g/L/h vs men 0.15-0.17
• Food: slows gastric absorption but not elimination rate
• Liver disease: cirrhosis/hepatitis −30-50%. Time-to-zero table from initial BAC (to reach 0.0): 0.5 g/L → 3.3 hours; 0.8 → 5.3; 1.0 → 6.7; 1.5 → 10; 2.0 → 13.3; 3.0 → 20 hours (note: safe driving time is BAC 0.0, NOT 0.5; reaction+coordination compromised even at 0.3). Coffee-cold shower-physical activity DO NOT speed up: alcohol is eliminated 90% by liver (ADH oxidation) and 10% urine-breath-sweat at fixed rate. Breathalyzer measures expired air alcohol (0.21 mg/L air = 0.5 g/L blood, conversion factor 1:2300). Italian police models: Dräger Alcotest 7110 MK III IT (Lübeck Germany, omologated DM 22/5/1990), AlcoQuant 6020

Women, elderly, minors: specific risks

Women have BAC 30-40% higher at equal alcohol+weight vs men due to: 1) lower TBW: women 50% vs men 60% body weight (more adipose tissue, less muscle); 2) lower gastric ADH Frezza-Lieber 1990 NEJM 322:95: women 1st-pass effect 23% vs men 38%; 3) menstrual cycle luteal phase reduced clearance (Sutker 1987 Alcohol Clin Exp Res 11:74). Consequences: at equal consumption, women 2× cirrhosis risk, 2.4× pancreatitis, 1.5× cardiomyopathy (NIAAA 2021). Elderly >65: TBW reduced to 50%, hepatic CYP2E1 −30%, polypharmacy interactions (BDZ benzodiazepines + alcohol respiratory depression, warfarin + alcohol hemorrhage); recommendation max 1 UA/day over-65 (NIAAA 2020). Adolescents 14-17: developing brain (prefrontal cortex matures at 25), alcohol damages memory-hippocampus (DeBellis 2000, Tapert 2002), binge drinking + adult dependence association 4× (Squeglia 2014). Italian L. 189/2012 art. 7: alcohol sale to <18 forbidden, fines 250-1,000 € (vendor) + 15 days closure; ID check mandatory. Italian L. 125/2001 "alcohol framework law": free SerD addiction service in ASL public health, AA Alcoholics Anonymous self-help groups (1,200 groups Italy).

Updated July 2026