Estimateur de taux d'alcool dans le sang (TAS)

The Widmark formula estimates blood alcohol concentration as BAC = (A / (W × r)) × 100, where A is the mass of pure alcohol consumed in grams, W is body weight in grams, and r is a distribution ratio that reflects how much of the body is water (alcohol diffuses into water, not fat). Erik Widmark first published the formula in Sweden in 1932. The result is a percentage of alcohol by mass in the blood.

On average, female bodies have a higher proportion of body fat and a lower proportion of body water than male bodies, so the same amount of alcohol distributes into less water and reaches a higher concentration. The Widmark r constant captures this difference: roughly 0.68 for males and 0.55 for females. Individual r varies by body composition, so two people of the same sex and weight can still reach different BACs from identical drinks.

Healthy adults metabolize alcohol at roughly 0.015 BAC per hour on average, mostly via the liver enzymes alcohol dehydrogenase and aldehyde dehydrogenase. The rate is roughly linear (zero-order kinetics) once BAC is above about 0.02. Real-world elimination is faster in heavy drinkers, slower with certain genetic variants, and slowed further by liver disease, fatigue, or some medications.

A US standard drink contains 14 grams (about 0.6 fl oz) of pure ethanol. That works out to roughly 12 oz of regular beer at 5% ABV, 5 oz of wine at 12% ABV, or 1.5 oz of 80-proof (40% ABV) spirits. Standard-drink definitions vary internationally: the UK uses 8 g per unit, Australia uses 10 g, and Japan uses 20 g.

In the United States, a BAC of 0.08% per se constitutes driving under the influence in every state for drivers 21 and older (Utah lowered its limit to 0.05% in 2018). The 0.08 threshold was adopted nationwide by 2004 after research showed measurable impairment of reaction time, divided attention, and lane control at that level. Commercial drivers face a 0.04% limit, and drivers under 21 face zero-tolerance laws.

Real BAC depends on dozens of factors no estimator can capture: rate of consumption, stomach contents and meal timing, hydration, body composition versus raw weight, liver health, recent sleep, medications, hormones, and individual enzyme variants. Field studies show Widmark estimates can be off by 30% or more in either direction. Use this tool to think about pacing and recovery time, never as evidence that you're safe to drive.