Alcohol Units & Widmark BAC Calculator
Calculate blood alcohol concentration (BAC) using the clinical Widmark formula, UK units, US standard drinks, and hours to sober.
Legal Blood Alcohol Limits for Driving
⚠ Critical Safety & Legal Notice
This calculator provides a mathematical estimate based on the Widmark clinical formula. Actual BAC varies significantly with stomach fullness, liver enzyme health, medication, and metabolism. Never drink and drive. If you have consumed alcohol, always arrange a taxi or designated driver.
About this tool
How to use it
- Select your biological sex (to establish body water distribution) and enter your current body weight.
- Enter the hours elapsed since your first alcoholic beverage was served.
- Use the + and - buttons to count beers, wines, spirit shots, or craft IPAs consumed.
- Read your estimated Blood Alcohol Concentration (BAC), UK units, US standard drinks, and hours until 100% sober.
Why it matters
Many people assume having a cup of coffee or drinking a glass of water speeds up alcohol clearance. In reality, the liver metabolizes ethanol at a fixed biological rate (approximately 0.015% BAC or 1 UK unit per hour). Understanding this scientific rate prevents dangerous next-morning drink-driving incidents.
When to use it
Use this calculator the morning after a night out before commuting, when planning responsible dinner drinking, or estimating the alcoholic units in various craft beers and wine bottles.
Good to know
Swedish physician Erik Widmark developed the Widmark formula in 1932. One UK unit contains exactly 8 grams of pure ethanol, whereas one US standard drink contains 14 grams (0.6 fluid ounces).
Common questions
How fast does the human body metabolize alcohol?
On average, the human liver clears alcohol at a constant rate of approximately 0.015% BAC per hour (or about one standard unit of alcohol per hour). Sleep, cold showers, and coffee cannot speed up this hepatic enzymatic breakdown.
What is the legal drink-driving limit in the UK and US?
In the United States, England, Wales, and Northern Ireland, the statutory limit is 0.08% BAC (80 mg per 100 ml of blood). In Scotland and most European countries, the legal limit is stricter at 0.05% BAC.
Can I still be over the limit the morning after drinking?
Yes. If someone finishes drinking at 2:00 AM with a peak BAC of 0.15%, their blood alcohol level will still be around 0.06% to 0.07% at 8:00 AM, making driving illegal or dangerous on their morning commute.
Why do men and women have different BAC levels from the same drink?
On average, women have a lower percentage of body water (55% vs 68% in men) and lower concentrations of gastric alcohol dehydrogenase enzymes, resulting in a higher concentration of alcohol in the bloodstream for equivalent drinks.