Blood Alcohol (BAC) Calculator
Estimate blood alcohol content. An estimate only, never for driving.
One US standard drink = 14 g of pure alcohol (a 12 oz 5% beer, 5 oz wine, or 1.5 oz spirit).
Time elapsed since your first drink. The model assumes a 0.015 percentage-point decrease per hour; your actual rate can differ.
Estimated BAC
- Effect band
- At or over the 0.08% US driving limit
- Pure alcohol consumed
- 56 g
This is an estimate only and must never be used to decide whether it is safe to drive. There is no safe way to calculate that you are under a legal limit. If you have been drinking, do not drive.
Rough estimate from the Widmark equation. Your real BAC depends on food, drink strength, pace, medication, and your own metabolism, and can be much higher than shown.
How the BAC calculator works
This tool produces a rough blood alcohol concentration (BAC) scenario using a simplified Widmark equation. It is not a measurement. In the United States, most states use 0.08 g/dL as the per-se limit for adult drivers, while Utah uses 0.05 g/dL and lower or different limits can apply to drivers under 21, commercial drivers, or other situations. Impairment begins below those limits.
The calculation has two parts. First it finds the peak concentration from the alcohol in your system, then it subtracts what your body has cleared over time.
The grams of pure alcohol come from your drink count: alcoholGrams = drinks * 14, since one US standard drink holds about 14 grams. That alcohol distributes through your body water, which the model approximates as weightKg * 1000 grams scaled by a distribution ratio r (0.68 for men, 0.55 for women). The peak is (alcoholGrams / (weightKg * 1000 * r)) * 100. Finally, because the body eliminates roughly 0.015% per hour, the tool subtracts 0.015 * hours since your first drink. The result is floored at zero, since you can never have a negative amount of alcohol in your blood.
Worked example
A man weighing 80 kg has 4 standard drinks, and it has been 1 hour since his first.
- Alcohol consumed:
4 * 14 = 56 g - Body water term:
80 * 1000 * 0.68 = 54,400 - Peak BAC:
(56 / 54,400) * 100 = 0.103% - Eliminated in 1 hour:
0.015 * 1 = 0.015 - Estimated BAC:
0.103 - 0.015 = 0.088%
At about 0.088%, the scenario is above the general 0.08 g/dL US per-se limit. Two additional hours in
the model increase the elapsed-time term to 0.015 * 3 = 0.045, leaving
0.103 - 0.045 = 0.058%. That lower modeled result is not permission to drive: legal limits vary and
driving ability can be impaired below them.
How to use it
- Count your standard drinks honestly. A large glass of wine or a strong cocktail can be two drinks or more, so round up when unsure.
- Enter your body weight. You can switch between kilograms and pounds with the unit toggle; pounds are converted to kilograms before the math runs, so the result is the same either way.
- Choose your sex, which sets the distribution ratio in the formula.
- Enter the hours since your first drink, which drives how much alcohol your body has had time to clear.
Limitations and safety
This calculator is for general education only. It is not a breathalyzer, blood test, medical device, or legal advice. Drink size and strength, timing, food, absorption, body composition, medication, illness, and individual metabolism can make the true concentration materially higher or lower.
Do not use this result to decide whether to drive, operate machinery, supervise others, swim, or do anything where impairment creates danger. If you have been drinking, arrange a sober driver, taxi, rideshare, or public transport. If someone is difficult to wake, breathing slowly or irregularly, vomiting repeatedly, confused, having a seizure, or showing pale or blue-tinged skin, seek emergency medical help rather than relying on this calculator.
Sources and scope
- Jurisdiction
- United States definitions and driving-law context
- Data current to
- July 30, 2026
- Last updated
- What's a standard drink? — National Institute on Alcohol Abuse and Alcoholism
- Drunk Driving — National Highway Traffic Safety Administration
- Impaired Driving — Centers for Disease Control and Prevention
Frequently asked questions
Can I use this to check whether I am safe to drive?
No. This is an estimate, not a measurement, and it can be wrong by a wide margin in either direction. The only honest answer is that if you have been drinking, you should not drive. No calculator can tell you that you are under a legal limit, because the real figure depends on details this tool cannot know. Treat any result above zero as a reason not to get behind the wheel.
What counts as one standard drink?
In the United States a standard drink contains about 14 grams of pure alcohol. That is roughly a 12 ounce beer at 5 percent, a 5 ounce glass of wine at 12 percent, or a 1.5 ounce shot of spirits at 40 percent. Cocktails, craft beers, and large pours often hold more than one standard drink, so count generously rather than optimistically.
Why does the same number of drinks give a woman a higher result?
This simplified Widmark implementation uses different average alcohol-distribution constants for its two sex settings. They are population-level assumptions, not measurements of an individual person's body water or metabolism. The binary input and fixed constants cannot represent every body, which is one reason the result can differ materially from a breath or blood test.
How fast does the body clear alcohol?
This calculator assumes a fixed decrease of 0.015 percentage points per hour. That is a modeling assumption, not a measurement of your personal elimination rate. Real absorption and elimination vary, so waiting until the displayed result reaches zero is not proof that no alcohol remains or that driving is safe.
Why might my real BAC be higher than the estimate?
The Widmark model assumes alcohol is fully absorbed and uses average constants. Drinking on an empty stomach, drinking quickly, stronger drinks than you counted, medication, illness, and individual metabolism can all push your true concentration above the figure shown. Because of that, a low estimate is never a green light.