Blood Alcohol Content (BAC) Calculator
Estimate your blood alcohol content (BAC) with the Widmark formula from the number of drinks, your weight, sex, and time elapsed. For education only — never drink and drive.
⚠️ For education only — never use this to decide if you can drive. If you have been drinking, do not drive.
Estimated BAC
0.055%
Reduced coordination & judgment
Time to reach 0.00%
3h 40m
at ~0.015%/hour
Legal driving limit
0.08%
You are under the limit (estimate)
The Widmark formula is a rough estimate that ignores food, hydration, medication, and individual metabolism. Never rely on it to decide whether to drive.
Frequently Asked Questions
What is the Widmark formula for BAC?
The Widmark formula estimates blood alcohol content: BAC = (alcohol grams ÷ (body weight grams × r)) × 100, minus the alcohol your body has metabolized over time. 'r' is the body-water distribution ratio — about 0.68 for men and 0.55 for women. The body clears roughly 0.015% BAC per hour.
What counts as one standard drink?
In the U.S., one standard drink contains about 14 grams of pure alcohol: a 12 oz beer at 5%, a 5 oz glass of wine at 12%, or a 1.5 oz shot of 40% (80-proof) spirits. Cocktails and craft beers often contain more than one standard drink.
How long does it take for alcohol to leave your system?
On average the body eliminates alcohol at about 0.015% BAC per hour, regardless of coffee, water, or food. So a BAC of 0.08% takes roughly 5–6 hours to reach zero. Only time lowers BAC — nothing speeds it up meaningfully.
What is the legal BAC limit for driving?
In all U.S. states the limit is 0.08% for drivers 21 and over (0.05% in Utah), with zero-tolerance laws for those under 21. Impairment begins well below the legal limit, so the safest driving BAC is 0.00%.
How accurate is a BAC calculator?
Widmark estimates are approximate and vary with metabolism, food, hydration, medications, sex, and individual differences. They can be off by a wide margin and must never be used to decide whether it's safe to drive. This tool is for education only.