Blood Alcohol (BAC) Calculator
A rough estimate of your blood alcohol level, and how long it takes to fall to zero.
Good to know. Coffee, cold showers and fresh air don’t speed it up. Only time does.
Not medical advice. A general estimate for healthy adults.
How it works
In plain words
Add up the pure alcohol in the drinks. Divide it by your body weight times the share of your body that holds water (about 68% for men and 55% for women), then take off about 0.015% for each hour since you started drinking.
The formula
alcohol (g) = volume × strength × 0.789 BAC % = alcohol ÷ (weight in g × r) × 100 − 0.015 × hours r ≈ 0.68 men, 0.55 women
Worked example
Three 330 ml beers at 5% hold about 39 g of alcohol. For a 75 kg man: 39 ÷ (75,000 × 0.68) × 100 = 0.077%, minus 2 × 0.015, is about 0.047%.
Sources
- Widmark, Die theoretischen Grundlagen und die praktische Verwendbarkeit der gerichtlich-medizinischen Alkoholbestimmung, 1932 The Widmark formula for blood alcohol.
- NIAAA, What is a standard drink? 14 g of pure alcohol per US standard drink.
- NHTSA, Drunk driving The 0.08% limit and effects at lower levels.
Sources checked September 30, 2026. 4 automated tests check its answers on every change.
About the blood alcohol (BAC) calculator
Blood alcohol concentration, BAC, is the share of alcohol in your blood. It is written as a percentage in the US (0.08%) and in grams per litre, or per mille, in much of Europe (0.8‰). This calculator estimates it with the Widmark formula, the classic method used in forensic science, from what you drank, your weight and sex, and the time since you started.
The same drink raises BAC more in a lighter person, and more in women than in men of the same weight, because women on average have less body water for the alcohol to spread into. The liver then clears about 0.015% an hour, roughly one drink an hour, and nothing speeds that up: not coffee, water, food after the fact or sleep.
Treat the result as a rough estimate. Real levels vary widely with food in the stomach, how fast you drink, medication, health and genetics, and can be well above the estimate. Drinks poured at home are often larger than the standard sizes used here.
Never use a calculator to decide whether to drive. Legal limits are 0.08% in most of the US and in England and Wales, 0.05% in Scotland and most of Europe, and 0.02% or zero in several countries and for new drivers. Impairment starts well below any limit. If you have been drinking, don’t drive, and remember you may still be over the limit the next morning.
Questions people ask
How long does it take for alcohol to leave your body?
About one hour per standard drink: BAC falls by roughly 0.015% an hour. A BAC of 0.08% takes over 5 hours to reach zero.
How many drinks put you over 0.08%?
For many men, 3 to 4 drinks in an hour; for many women, 2 to 3. It varies a lot, so the only safe number for driving is none.
What is 0.5 per mille in percent?
0.05%. Per mille is grams of alcohol per litre of blood; divide by 10 for the US percentage.