Free UK blood alcohol calculator that estimates your BAC against the 80mg/100ml drink-drive limit in England, Wales and Northern Ireland and the 50mg/100ml limit in Scotland. The calculator uses 8-gram UK standard units (the smallest in the developed world), the Widmark formula, and supports weight in kg or stones. UK unit reference: a pint of 5% lager is roughly 2.8 units, a 175ml glass of 13% wine is about 2.3 units, a 25ml shot of spirits is 1 unit. The UK Chief Medical Officers' guideline is no more than 14 units per week, spread over three or more days. Your liver clears about 1 UK unit per hour, so a four-pint Friday night ending at midnight (around 11 units) does not return to zero BAC until roughly 11am the following morning — which is why morning-after drink-drive convictions are common in the UK. Sources: GOV.UK Drink Drive Limit, Transport Scotland, Department for Transport, NHS Alcohol Units. This calculator is for educational use only — never rely on an estimate to decide whether to drive.