BAC Calculator: A Math Estimate, Not a Green Light
| Scenario | Est. BAC now | Hours to zero |
|---|---|---|
| 180 lb male, 3 drinks, 1.5 h in | 0.053% | 3.5 h |
| 140 lb female, 2 drinks, 1 h in | 0.065% | 4.3 h |
| 200 lb male, 4 drinks, 2 h in | 0.061% | 4.1 h |
| 120 lb female, 3 drinks, 2 h in | 0.110% | 7.4 h |
| 140 lb female, 2 drinks, 0 h (right after) | 0.080% | 5.3 h |
| 180 lb male, 3 drinks, 0 h (right after) | 0.076% | 5.1 h |
Blood alcohol content is simple chemistry wearing a uniform: grams of alcohol in, distribution across body water, metabolism out at a fairly steady rate. The Widmark equation above is the same one used in toxicology courses - alcohol grams divided by your body-water volume, minus about 0.015% per hour of drinking time. A US standard drink is 14 grams of pure alcohol, which is one 12-ounce beer at 5%, one 5-ounce glass of wine at 12%, or one 1.5-ounce shot at 40%.
What the math cannot know is you. Food in the stomach, medication, hydration, liver differences and drink pouring all move real BAC against the estimate - sometimes by a lot. That is why this page ends the way it does: the calculator exists to show how slowly alcohol clears and how much a single drink moves the number, not to green-light a car key. If you have been drinking, the answer to "can I drive yet" is no; the useful question this tool answers is how long until that stops being true.
How to use
- Count standard drinks honestly - a heavy-poured double is two, a 16-ounce craft IPA at 8% is closer to two and a half, and mixed drinks hide their shots.
- Enter your weight and sex (they set the Widmark body-water factor), then the hours since your first drink, since metabolism runs on elapsed time, not on when you stopped.
- Read the clear-time figure with a margin: the 0.015%/hour burn rate is an average, and slower metabolizers run behind it - add an hour before you trust a zero.
Frequently asked questions
How accurate is the Widmark equation?
For a healthy adult with standard drinks and honest inputs, it lands within roughly 0.01-0.02% of a real breathalyzer most of the time - useful for planning, not for proving. The error bars grow with unusual body composition, full versus empty stomach, and any medication, which is exactly why no estimate should ever clear you to drive.
How long does it take to sober up completely?
The average body burns about 0.015% BAC per hour, so the calculator's clear-time figure is simply your estimated BAC divided by 0.015. Two drinks at midnight for a 160-pound man reads roughly 0.05% - about three and a half hours to zero. Coffee, cold showers and food change how awake you feel, not the chemistry; only time moves the number.
Why does the same drink count hit women harder?
Body water, not body weight, is what dilutes alcohol, and on average women carry less water per pound - the Widmark distribution factor is 0.55 versus 0.68. Hormonal cycle timing adds further variation. The calculator's sex switch is a population average; individual bodies wander from it, which is another reason the estimate stays an estimate.
What counts as one standard drink?
In the US: 14 grams of pure alcohol. That is 12 ounces of regular beer at 5%, 5 ounces of wine at 12%, or 1.5 ounces of 40% spirits - per the National Institute on Alcohol Abuse and Alcoholism. Craft beer at 8-10% and generously poured wine can count as 1.5-2.5 standard drinks per serving, which is the single biggest source of underestimating.
Can I use this to decide if I'm okay to drive?
No - and every serious version of this tool says so, including this one. Real BAC varies with food, sleep, medication and individual metabolism enough that an estimate within a few hundredths still spans legal and illegal. If the estimate says 0.02 or 0.12, the driving answer is the same: call a ride. The legitimate use is planning tomorrow morning and understanding how long impairment lingers after the last drink.