Calculate blood alcohol content using the Widmark formula: current BAC in per mille, time until sober and until below legal limits.
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Calculating Blood Alcohol: The Widmark Formula Explained
This calculator uses the classic formula of forensic scientist Erik Widmark: per mille = alcohol in grams ÷ (body weight × distribution factor). The factor is about 0.68 for men and 0.55 for women, because alcohol only distributes in body water. A resorption deficit of 15% is also deducted – part of the alcohol never reaches the bloodstream.
A worked example
A man weighing 80 kg drinks three half-litres of beer (5%). That is 3 × 500 ml × 0.05 × 0.8 g/ml = 60 g of pure alcohol. With the resorption deficit: 60 × 0.85 ÷ (80 × 0.68) ≈ 0.94 ‰ at the end of drinking. After two hours of elimination (2 × 0.15 ‰) around 0.64 ‰ remain – well above the German 0.5 ‰ limit. From that point, full sobriety is still more than four hours away.
German road traffic limits
From 0.5 ‰ you commit a regulatory offence (fine, points, driving ban); from 1.1 ‰ absolute unfitness to drive applies – a criminal offence even without driving errors. As early as 0.3 ‰, relative unfitness can be assumed if there are signs of impairment or an accident. Novice drivers on probation and drivers under 21 face a strict 0.0 ‰ limit.
Why these are estimates only
Actual blood alcohol depends on factors no formula captures: stomach contents, drinking speed, medication, liver function, fatigue. Elimination also varies individually between 0.1 and 0.2 ‰ per hour – we use the average of 0.15 ‰. Coffee, cold showers or exercise do not speed it up. Never use the result as clearance to drive: if you have been drinking, leave the car parked.
