Kalkulo

Blood alcohol calculator

Estimate your blood alcohol level with the Widmark formula from UK units against the 80 mg/100 ml limit. Educational only, never a basis for driving.

Result
0.061 %BAC
Below legal limit (0.08 %BAC)
Time to full elimination: ~4.1 h
Indicative only. Never drink and drive.

About this tool

Why use this tool

The Blood Alcohol Concentration (BAC) calculator estimates the alcohol level in your bloodstream. It highlights UK drink-drive limits: 80 mg alcohol per 100 ml blood (equivalent to 0.8 g/L) in England, Wales and Northern Ireland; 50 mg/100 ml (0.5 g/L) in Scotland. Enforced by the Road Traffic Act 1988 and Police Scotland.

How the calculation works

Widmark formula: BAC(g/L) = alcohol(g) ÷ (weight(kg) × r), r = 0.7 for men and 0.6 for women. A UK unit of alcohol = 10 ml (8 g) of pure alcohol per NHS definition. A pint of 4 % beer = 2.3 units, a 175 ml glass of 12 % wine = 2.1 units, a 25 ml spirits shot at 40 % = 1 unit. Liver elimination averages 0.15 g/L per hour but varies widely.

Real example

A 12-stone (76.2 kg) man drinking 4 UK units (roughly 2 pints of 4 % beer) = 32 g alcohol. BAC = 32 ÷ (76.2 × 0.7) = 0.60 g/L = 60 mg/100 ml — legal in England but over the Scottish limit. A 10-stone (63.5 kg) woman with 3 units = 24 g: BAC = 24 ÷ (63.5 × 0.6) = 0.63 g/L = 63 mg/100 ml — again over Scotland's 50 mg limit.

Practical tips

Never drive after drinking. Use public transport, a taxi or a designated driver. Coffee, food after drinking and cold showers do not reduce BAC — only time does. The NHS recommends no more than 14 units per week spread over 3+ days. Drink Aware (drinkaware.co.uk) offers free calculators and advice. Alcohol Change UK campaigns for safer limits. Sentences for drink-driving: minimum 12-month driving ban, £5,000 fine, up to 6 months prison.

Disclaimer

This calculator is for education only. It does not model absorption speed, food intake, medications, fatigue or medical conditions. Never use it to decide whether to drive — police roadside breathalysers are the only legal test. If you're worried about your drinking, contact Drinkline (0300 123 1110) or your GP for referral to NHS alcohol services.

Frequently asked questions

What is a UK unit of alcohol?⌄
The NHS defines one UK unit as 8 grams (10 ml) of pure alcohol. A pint of average-strength (4%) lager is about 2.3 units, a large 250 ml glass of 13% wine is roughly 3.25 units, and a single 25 ml pub measure of 40% spirits is 1 unit — so a typical night out can add up faster than most people expect.
What is the legal drink-drive limit in England, Wales and Northern Ireland?⌄
The limit is 80 milligrams of alcohol per 100 millilitres of blood, set by the Road Traffic Act 1988. Scotland set a lower limit of 50 mg per 100 ml in 2014, so a level that is legal to drive on in England can already be over the limit north of the border — always check the current limit for where you are driving.
Does the 'one hour per unit' rule for sobering up actually work?⌄
It is a rough average, not a reliable countdown. Liver processing speed varies by body weight, sex, liver health and metabolism, and averages around 0.15 g/L per hour, so relying on a fixed hours-per-unit rule can significantly underestimate how long alcohol actually stays in your system.
Do coffee or a cold shower reduce my BAC faster?⌄
No. Neither coffee, a cold shower, exercise nor fresh air speeds up how quickly the liver breaks down alcohol — they may make you feel more alert without actually lowering your blood alcohol level, which is part of why drink-driving remains dangerous even when someone feels fine.
Can this calculator replace a roadside breathalyser?⌄
No. This tool is for education only and does not account for your exact absorption rate, medication, fatigue or liver function, so it cannot reliably predict your true reading. Police breath, blood or urine tests are the only legal measure of your alcohol level — never use this calculator to decide whether it is safe to drive.

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