Blood Alcohol Content Calculator
Estimate your current blood alcohol level using the Widmark formula. This is an educational tool — individual metabolism varies widely and this should never be used to decide whether to drive.
Blood Alcohol Content Guide
UK Drink Drive Limits
England, Wales, and Northern Ireland: 80mg per 100ml blood (0.08% BAC) — one of the highest limits in Europe. Scotland: 50mg per 100ml blood (0.05% BAC). Professional drivers (HGV, bus): 0.02% BAC across the UK. Many other European countries use 0.05% or 0.02% limits. The safest approach is not to drink any alcohol before driving — individual metabolism varies so widely that there is no reliable 'safe' number of drinks.
How BAC Is Calculated
The Widmark formula estimates BAC: alcohol consumed (grams) divided by (body weight in grams times distribution factor). The distribution factor is 0.55 for women and 0.68 for men — reflecting difference in average body water percentage. Women typically reach higher BAC than men from the same amount of alcohol. BAC reduces at approximately 0.015% per hour as the liver metabolises alcohol (roughly one standard unit per hour). Eating, coffee, water, and exercise do not speed this up.
BAC and Impairment
0.02–0.03%: relaxation, slight warmth, slowed reaction time beginning. 0.05–0.06%: coordination affected, visual tracking reduced — impaired even below the English limit. 0.08%: significantly impaired judgment, coordination, and reaction time. 0.10%: major motor impairment. 0.15%: nausea, severe impairment. 0.30%: risk of unconsciousness. Above 0.40%: potentially fatal. Impairment begins well below the legal limit — research consistently shows driving ability is affected from 0.02% BAC.
Factors That Affect BAC
Body weight: heavier people reach lower BAC from the same amount. Body composition: more muscle = more body water = lower BAC per drink. Sex: women have lower distribution factor and often less alcohol dehydrogenase enzyme. Food: eating before and during drinking slows absorption significantly. Drink speed: faster drinking = higher peak BAC. Tolerance: experienced drinkers may feel less impaired at the same BAC but are equally dangerous behind the wheel. Medications: many common medications ampl
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