Estimate your blood alcohol level using the Widmark formula in seconds.
BAC stands for blood alcohol content — the percentage of alcohol in your bloodstream. This calculator uses the Widmark formula to estimate it from your drinks, weight, sex, and time elapsed since the first drink.
When to use this calculator
- You want a rough estimate of your BAC after a few drinks.
- You're planning how long to wait before driving (educational only).
- You want to understand how weight, sex, and time affect alcohol levels.
How it works
The calculator uses the Widmark equation: BAC = (alcohol grams ÷ (body weight × distribution ratio r)) − (β × hours). The distribution ratio r is about 0.68 for men and 0.55 for women. Alcohol elimination β is roughly 0.015% per hour. One US standard drink contains about 14 g of pure alcohol — so 3 standard drinks equal 42 g.
Real-world examples
- Designated-driver planning: a 70 kg adult who had 3 standard drinks 2 hours ago lands near 0.04% — a useful general check, never a legal one.
- Personal awareness: comparing BAC after 2 wines vs 2 beers shows that strength and serving size matter as much as drink count.
- Health education: the same 3 drinks produce a much higher BAC in a 60 kg person than in a 90 kg person of the same sex.
Limitations
- Widmark is a simplified model — real BAC depends on food, hydration, medications, genetics, and tolerance.
- Not a substitute for a breathalyser or blood test, and never proof of legal sobriety.
- Results are estimates only and must not be used to decide whether you can drive.
- Body fat percentage and stomach contents at the time of drinking are not modelled.
Frequently asked questions
What is BAC?
Blood alcohol content — the percentage by volume of alcohol in your bloodstream. A BAC of 0.08% means 0.08 g of ethanol per 100 mL of blood.
How is BAC calculated here?
The calculator uses the Widmark formula with your weight, sex, number of standard drinks, and hours since the first drink to estimate current BAC.
Is this calculator legally accurate?
No. It is an educational estimate. Only a calibrated breathalyser or blood test is legally recognised; never use this number to decide whether you can drive.
What factors affect BAC the most?
Body weight, sex, number and strength of drinks, time elapsed, food in the stomach, hydration, and individual metabolism all noticeably change real BAC.
Why do men and women get different results from the same drinks?
Women generally have a lower distribution ratio and less alcohol dehydrogenase, so the same amount of alcohol typically produces a higher BAC than in a man of the same weight.
Related calculators
