BAC Calculator
Estimate blood alcohol content with the Widmark formula from your weight, sex, drinks, and hours elapsed. A rough estimate only — it cannot determine legal sobriety. Never drink and drive.
How long until you're sober? This calculator estimates your blood alcohol content (BAC) using the Widmark formula — the same equation behind most alcohol estimation charts — from your body weight, sex, number of standard drinks, and time elapsed. It also estimates hours until your BAC reaches zero and flags where you stand relative to the 0.08% US driving limit. Read the warnings: this is a rough estimate that cannot determine whether you are legally sober or safe to drive.
Never drink and drive. This is a rough estimate only — it cannot determine legal sobriety or whether you are safe to drive. When in doubt, don't.
How to use this calculator
- Enter your body weight in pounds.
- Select your sex (the formula's distribution factor differs).
- Enter the number of standard drinks (0.6 oz of pure alcohol each).
- Enter the hours since you started drinking.
- Click Calculate to see your estimated BAC, impairment tier, and estimated hours until sober.
The formula
Widmark: BAC% = max(0, (drinks × 0.6 × 5.14) / (weight_lbs × r) − 0.015 × hours), where r = 0.73 for men and 0.66 for women. Hours until sober ≈ BAC / 0.015.
Worked example
A 180-pound man who has 4 standard drinks over 2 hours has an estimated BAC of 0.064% — below the 0.08% US driving limit but firmly in impairment territory, needing about 4.3 more hours to reach zero. He should not drive.
Frequently Asked Questions
How does the Widmark formula estimate BAC?
The Widmark formula converts your drinks into grams of alcohol, divides by your body's water volume (estimated from weight and a sex-based distribution factor: 0.73 for men, 0.66 for women), and subtracts alcohol eliminated over time at roughly 0.015% per hour. It's the standard textbook method for BAC estimation. But it assumes average metabolism, average absorption, and standard drink sizes — all of which vary widely in real life.
What is the legal BAC limit for driving?
In all 50 US states, 0.08% is the per se limit for drivers 21 and over — at or above it, you're legally impaired regardless of how sober you feel. Limits are stricter for commercial drivers (0.04%) and drivers under 21 (0.00–0.02% depending on the state). Other countries are often stricter still. And crucially: impairment of judgment and reaction time begins well below 0.08%, so 'under the limit' is not the same as 'safe to drive.'
Why can't this calculator tell me if I'm sober enough to drive?
Because it can't measure what's actually in your blood. Real BAC depends on your exact drink sizes and strengths, how fast you drank, how much food was in your stomach, your individual metabolism, medications, fatigue, and tolerance — none of which a web form can know. Two people entering identical numbers can have meaningfully different BACs. The only safe rule is: if you've been drinking, don't drive. Arrange a ride.
Why do weight and sex change the result so much?
Alcohol distributes through body water, not fat, so a heavier person dilutes the same amount of alcohol in more fluid and ends up with a lower BAC. Women on average have a higher proportion of body fat and lower body water than men of the same weight, which is why the formula uses a smaller distribution factor (0.66 vs 0.73) — the same drinks produce a higher BAC. This is physiology, not judgment: smaller bodies get drunker faster.
What counts as one standard drink?
In the US, one standard drink contains about 0.6 ounces (14 grams) of pure alcohol: 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% (80-proof) spirits. Real-world pours are often bigger — a generous wine glass or a strong cocktail can easily be two standard drinks. When in doubt, count up: underestimating your drinks is the most common way these estimates come out too low.