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.
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Blood Alcohol Content Guide
What do I need to know about 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.
What's the key thing to understand about 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.
What should I know about 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 amplify alcohol's effects, and some — including certain painkillers and sedatives — can be dangerous in combination even at BAC levels that would otherwise seem manageable.