Blood Alcohol Content (BAC) Calculator
Estimate your current blood alcohol content using the Widmark formula. For educational purposes only — never use to decide whether to drive.
What is Blood Alcohol Content (BAC)?
BAC is the concentration of alcohol in the bloodstream, expressed as a percentage (e.g., 0.08% = 0.08 g of alcohol per 100 ml of blood). The Widmark formula estimates BAC from body weight, the Widmark r factor (body water distribution), alcohol consumed, and time elapsed as the liver metabolises alcohol at approximately 0.015% per hour.
Legal BAC Limits by Country
| Country | Limit (BAC %) | Notes |
|---|---|---|
| USA | 0.08% | 0.04% for commercial drivers |
| United Kingdom | 0.08% (England/Wales) | 0.05% in Scotland |
| Germany | 0.05% | 0.00% under age 21 |
| France | 0.05% | 0.02% for new drivers |
| Japan | 0.03% | Strict enforcement |
| Australia | 0.05% | 0.00% for learner drivers |
| Canada | 0.08% | 0.05% administrative suspension |
Action Tips
- If your estimated BAC is above 0.05%, do not drive — arrange a taxi, rideshare, or designated driver.
- Drink water between alcoholic drinks to stay hydrated (does not lower BAC but reduces dehydration).
- Eat food before and during drinking — it significantly slows alcohol absorption.
- Wait at least 1 hour per 0.015% BAC before considering driving, and add a safety buffer.
- Sleep is the safest way to sober up — you metabolise alcohol even while asleep.
Frequently Asked Questions
How accurate is a BAC calculator?
Online BAC calculators using the Widmark formula are accurate to ±20–30% compared to a breathalyzer. Food, medications, body composition, and individual enzyme activity significantly affect results. Never use a calculator to decide if you are safe to drive.
How long does it take to sober up?
The average person eliminates approximately 0.015% BAC per hour. At a BAC of 0.08%, you would need roughly 5–6 hours to reach zero. Coffee, cold showers, and food do not speed elimination — only time does.
Does food affect BAC?
Yes, significantly. Eating before or during drinking slows alcohol absorption and can reduce peak BAC by up to 50%. However, food does not speed elimination of alcohol already in your blood.
What is the legal limit for driving?
Limits vary: USA 0.08%, UK 0.08% (Scotland 0.05%), Germany 0.05%, Japan 0.03%. Always check your local laws, and remember that any impairment is dangerous regardless of the legal limit.
Does gender affect BAC?
Yes. Women typically have a lower Widmark r factor (0.55 vs 0.68 for men) due to higher body fat percentage and lower total body water. The same number of drinks produces a higher BAC in women compared to men of equal weight.