After the party comes the question: how much alcohol is still in the blood? The Blood Alcohol Calculator uses the classic formula of forensic scientist Erik Widmark – and this tutorial explains the calculation, its limits and the legal situation.
The Widmark formula
Per mille = alcohol in grams ÷ (body weight × distribution factor). The distribution factor (0.68 for men, 0.55 for women) accounts for alcohol distributing only in body water. Added to this is a resorption deficit of around 15% – part of the alcohol never reaches the blood. The alcohol content of a drink: volume in ml × vol% × 0.8.
Step by step
- Enter sex and weight
- Count the drinks: beer (0.5 l ≈ 20 g of alcohol), wine (0.2 l ≈ 19 g), sparkling wine (0.1 l ≈ 9 g), spirits (4 cl ≈ 13 g)
- State the time since you started drinking: the body eliminates about 0.15 ‰ per hour
- Read the result: current value, peak value and waiting times until 0.5 / 0.3 / 0.0 ‰
Worked example
Man, 80 kg, three half-litres of beer: 60 g of alcohol × 0.85 ÷ (80 × 0.68) ≈ 0.94 ‰ at the end of drinking. After two hours around 0.64 ‰ remain – and full sobriety is another good four hours away. Important for driving the next morning: going to bed at 2 a.m. with 1.5 ‰ still means about 0.6 ‰ at 8 a.m.
The legal situation in Germany
From 0.5 ‰ a regulatory offence (€500 fine, 2 points, 1-month driving ban for a first offence), from 1.1 ‰ a criminal offence due to absolute unfitness to drive. As early as 0.3 ‰, signs of impairment or an accident can trigger criminal proceedings and licence withdrawal. Novice drivers and under-21s: strictly 0.0 ‰. And the most important limit of the calculation itself: no formula captures stomach contents, medication, fatigue and individual variation (elimination 0.1–0.2 ‰/h). The result is an orientation – never clearance to drive.
