Blood Alcohol (BAC) Calculator
Estimated blood alcohol content from drinks, weight, and time.
Input sheet
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Blood alcohol content estimates how much alcohol is in your bloodstream from the drinks you've had, your weight, sex, and how much time has passed. It's an educational estimate only — it should never be used to decide whether to drive.
How it works
Widmark formula: grams of alcohol ÷ (body weight in grams × distribution factor) × 100, minus ~0.015% per hour of metabolism.
The tool uses the Widmark formula: grams of alcohol divided by body weight in grams times a distribution factor (0.68 for men, 0.55 for women), expressed as a percentage, minus about 0.015% per hour as your body metabolizes it.
One standard drink is counted as 14 grams of pure alcohol — roughly a 12 oz beer, 5 oz of wine, or 1.5 oz of spirits. Real drinks vary in strength, which is one of many reasons the estimate can be well off for any individual.
BAC (%) = (grams of alcohol ÷ (body weight in grams × distribution factor)) × 100 − 0.015 × hours. One standard drink ≈ 14 g alcohol.
Worked examples
A 180 lb man, 4 standard drinks, 2 hours elapsed. → BAC about 0.071% — under the 0.08% legal limit, but impaired.
4 × 14 = 56 g; 56 ÷ (81,647 × 0.68) × 100 ≈ 0.101; − 0.015 × 2 = 0.071%.
A 140 lb woman, 3 standard drinks, 1 hour elapsed. → BAC roughly 0.10% — over the legal limit.
3 × 14 = 42 g; 42 ÷ (63,503 × 0.55) × 100 ≈ 0.120; − 0.015 ≈ 0.105%.
Tips & gotchas
- Treat any non-zero result as 'do not drive' — impairment starts well below the legal limit.
- Your body clears alcohol at a fixed rate of about one standard drink per hour; nothing speeds it up — not coffee, not a cold shower.
- Drinking on an empty stomach raises BAC faster; food slows but does not stop absorption.
- Stronger pours, cocktails, and craft beers often pack more than one standard drink, so the real total may exceed what you count.
FAQ
Is this safe to rely on for driving?
No. BAC estimates vary widely by person, food, and drink strength. If you have been drinking, do not drive — period.
Can I sober up faster to drive?
No. Only time clears alcohol, at roughly 0.015% per hour. Coffee, water, food, and showers may make you feel more alert but do nothing to lower your actual BAC.
Why do men and women get different results at the same weight?
Women generally have a lower proportion of body water to distribute alcohol into, reflected in the 0.55 versus 0.68 factor. The same drinks therefore produce a higher BAC on average.
How long until I'm completely sober?
Divide your estimated BAC by 0.015 to approximate the hours to reach zero. This is a rough figure — individual metabolism varies — so always err on the side of waiting longer.
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