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BAC / Alcohol Elimination Calculator
Estimate blood alcohol concentration (BAC) with the Widmark formula and how long until alcohol leaves your system.
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How to use this calculator
Enter your values after choosing the type of calculation in the tabs. The result updates as you type; press Calculate to confirm and jump to the result on mobile. Use Share to send the calculator with your result.
The Widmark formula
BAC (%) = alcohol (g) ÷ (r × body weight (g)) × 100 − β × hours
r ≈ 0.68 (men), 0.55 (women) β ≈ 0.015% per hour
Swedish chemist Erik Widmark developed this model in the 1930s and it’s still used in forensic estimates. r is the share of body weight that alcohol distributes into, and β is the average elimination rate (individuals range roughly 0.010–0.020% per hour). Example: a 176 lb (80 kg) man who has 4 standard drinks (56 g) over 2 hours: 56 ÷ (0.68 × 80,000) × 100 − 0.03 ≈ 0.073%.
What is a standard drink?
In the US a standard drink contains 14 grams of pure alcohol, per the National Institute on Alcohol Abuse and Alcoholism (NIAAA): 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits. Craft beers, large pours and cocktails often contain 1.5–3 standard drinks.
BAC and its effects
| BAC | Typical effects |
|---|---|
| 0.02% | Relaxation, some loss of judgment |
| 0.05% | Lower alertness, impaired coordination |
| 0.08% | US legal limit for drivers 21+; poor muscle control and reaction time |
| 0.15% | Far less muscle control, vomiting possible |
| 0.30% + | Risk of passing out, alcohol poisoning, death |
Only time lowers BAC. Coffee, cold showers and food after drinking don’t speed elimination. If someone has slow or irregular breathing, can’t be woken, or has bluish skin, call emergency services.
Frequently asked questions
How long does it take for alcohol to leave your system?
On average BAC falls about 0.015% per hour, so a BAC of 0.08% takes roughly 5–6 hours to reach zero.
How many drinks put you over 0.08?
It varies widely; for many people it’s about 3–4 standard drinks in an hour or two. Never rely on a calculator to decide whether to drive.
About this tool
- Written by
- [Author: to be assigned]
- Reviewed by
- Expert review pending
- Last updated
- 31 Oct 2026
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