Blood Alcohol Content (BAC) Calculator
This estimates your blood alcohol content (BAC) with the Widmark formula, from how much you drank, your weight and how long ago you started. Read the result as a rough guide to how alcohol works — not as permission to get behind the wheel.
Your numbers
Result
- Alcohol consumedgrams
- 42
| From now | Estimated BAC |
|---|---|
| Now | 0.06 |
| +1 h | 0.04 |
| +2 h | 0.03 |
| +3 h | 0.01 |
| +4 h | 0 |
Never use this to decide whether to drive
This is an estimate, and a rough one. Real BAC depends on food, hydration, medication, health, drinking speed and individual metabolism — variables no formula can capture. It can easily read lower than your true level. The only safe amount of alcohol before driving is none. If you have been drinking, do not drive; use a taxi, rideshare, public transport or a sober driver.
How the Widmark formula works
BAC is the alcohol in your blood as a percentage. The Widmark estimate is:
BAC = (alcohol in grams × 100) / (body weight in grams × r) − 0.015 × hours
where r is a distribution factor — about 0.68 for men and 0.55 for women, reflecting differences in body water. One US standard drink is 14 g of pure alcohol, and your body clears roughly 0.015% per hour, which is the subtraction at the end. That elimination rate is fixed — only time lowers BAC. Coffee, water and cold showers do nothing to it.
What the number means
In the United States it is illegal to drive at 0.08% or above (0.05% in many other countries, and lower or zero for commercial and young drivers). But impairment of reaction time and judgment begins well below any legal limit — often from the first drink. A low estimate here is not a safe estimate. Also note BAC keeps rising for 30–90 minutes after your last drink as alcohol is still being absorbed, so a reading taken now can climb.
Informational and educational result. Not a substitute for professional advice.
Frequently asked questions
Sources
- National Institute on Alcohol Abuse and Alcoholism (NIAAA) — What is a standard drink
- CDC — Impaired driving and BAC effects
- E.M.P. Widmark — alcohol pharmacokinetics (1932)
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