How to estimate blood alcohol content
- Choose your sex and enter your body weight.
- Enter how many of each drink you had and how many hours ago you started drinking.
- Read the estimated BAC as a percentage and in per mille, plus roughly when it reaches zero.
This is an educational estimate, not a breathalyser and not medical or legal advice. Do not use it to decide whether to drive, operate machinery or swim.
The Widmark formula
Blood alcohol content is estimated with the Widmark formula, developed by the Swedish scientist Erik Widmark in the 1930s and still used by forensic toxicologists: BAC = alcohol in grams ÷ (body weight in grams × r) × 100, minus about 0.015% for each hour since drinking began. The factor r reflects how much of the body is water: on average 0.68 for men and 0.55 for women, which is why the same drinks raise a woman's BAC more. Grams of alcohol are worked out from volume × strength × 0.789 (the density of ethanol).
Real results vary a lot. Food in the stomach slows absorption, BAC usually peaks 30–90 minutes after the last drink, the elimination rate ranges from roughly 0.010 to 0.025% per hour, and medications and liver health change everything. Studies comparing Widmark estimates with blood tests find errors of 20% or more for individuals. Drink-driving limits also differ: 0.08% in the USA, England and Wales, 0.05% in most of Europe and Australia, 0.02% or zero for new drivers in many places.
The calculation happens in your browser; nothing is recorded.
How long does it take to sober up?
The liver clears about one standard drink an hour on average. Nothing, including coffee, cold showers or sleep, speeds this up.
Can I be over the limit the next morning?
Yes. After a heavy night, alcohol can still be in your blood well into the next day.
What are the signs of alcohol poisoning?
Confusion, vomiting, seizures, slow or irregular breathing, blue-tinged skin or being unconscious. Call emergency services immediately.