BAC Calculator
This BAC calculator gives a rough, theoretical estimate of your blood alcohol concentration using the Widmark formula, based on what you drank, your weight and sex, and the time that has passed. It cannot tell you whether you are legally or safely able to drive. Real BAC varies widely from person to person, and impairment starts well below the legal limit. If you have been drinking, don’t drive.
Updated
Results
- Estimated peak BAC
- Peak, after first drink
- Time until estimate is below 0.08%Shown only while above 0.08%; not a sign you can drive
- Time until estimate reaches about 0Shown only while above zero; not proof you are unimpaired
- Pure alcohol (g)
- US standard drinks14 g each
- Widmark factor r
- Elimination rate used (% per hour)
| Reference level | BAC | Time from now |
|---|
Results are estimates. See the methodology below.
How to use the calculator
- Choose US (lb, fl oz) or metric (kg, mL) units, then select your sex and enter your weight.
- Enter your drinks either as standard drinks or with the drink builder: number of drinks, size of each and alcohol by volume (ABV) from the label. A third drink row is under the advanced options.
- Enter the hours since your first drink and the hours you spent drinking. The drinking time can’t be longer than the time since the first drink.
- Optionally, change the elimination rate (advanced options) to see how much the estimate depends on it.
The times until the estimate falls below 0.08% and reaches zero appear only while it is above those levels.
How the estimate works
The Widmark formula spreads the alcohol you drank through your body water and subtracts what has been eliminated:
BAC (%) = alcohol (g) ÷ (body weight (g) × r) × 100 − β × hours since first drink
- Alcohol: one US standard drink holds about 14 grams of pure alcohol (NIAAA). In the drink builder, grams = volume in mL × ABV × 0.789, the density of ethanol.
- r (Widmark factor): 0.68 for men and 0.55 for women.
- β (elimination): 0.015% per hour by default. Wisconsin’s state crime laboratory gives this as the average, with typical rates of 0.010 to 0.025 g/100 mL per hour.
Alcohol is treated as absorbed steadily while you drink, so the estimate peaks when you stop and then falls by β each hour. Real bodies differ: the same crime lab notes that peak BAC occurs 10 to 120 minutes after the end of drinking, and NIAAA warns that BAC can keep rising after someone stops drinking. If you drank very slowly, the model may show 0.000% throughout, which is a simplification.
Not modeled: food, medications, tolerance, health conditions, age, unfinished drinks or uneven drinking. Results are not a breath or blood test.
Examples
Man, 160 lb, 3 standard drinks over 1 hour, 2 hours after the first
The estimate is 0.055%, after a modeled peak of 0.070% at the 1-hour mark. The model reaches about zero in 3 h 40 min. With an elimination rate of 0.010 instead of 0.015, the same evening gives 0.065% and 6 h 31 min to zero.
Woman, 130 lb, 4 standard drinks over 2 hours, 3 hours after the first
The estimate is 0.128%, after a peak of 0.143%. The model needs 3 h 11 min more to fall below 0.08% and 8 h 31 min to reach about zero. Neither time tells her when she could drive.
Woman, 150 lb, two 16 fl oz beers at 7% over 2 hours
Those two pints hold 52.3 g of alcohol, or 3.7 standard drinks, not two. The estimate when she stops drinking is 0.110%.
Why this can’t tell you if you can drive
An estimate below 0.08%, or even 0.000%, does not mean you are fine to drive. NHTSA says even a small amount of alcohol can affect driving ability, and in 2024, 2,028 people were killed in alcohol-related crashes where a driver’s BAC was between .01 and .07 g/dL. At .08, crash risk increases exponentially. Your true BAC could be higher than the estimate. The only safe choice after drinking is not to drive: use a designated driver, a rideshare or public transit.
NIAAA notes that coffee, cold showers and walking do not reverse the effects of alcohol. If someone has trouble staying conscious, is vomiting, has seizures or slow breathing, call 911 right away.
Frequently asked questions
What is the legal BAC limit in the US?
It is illegal to drive with a BAC of .08 or higher in all 50 states, DC and Puerto Rico, except Utah, where the limit is .05. Commercial motor vehicle drivers may not perform safety-sensitive functions at 0.04 or more under federal rules. Driving can be impaired below these limits.
How accurate is a BAC calculator?
Not accurate enough to rely on. It applies averages to everyone, while absorption, body water and elimination vary between people and from night to night. Treat the result as an illustration, never as a measurement or a reason to drive.
What counts as one standard drink?
About 14 g of pure alcohol: 12 fl oz of regular beer at about 5%, 8–10 fl oz of malt liquor or hard seltzer at about 7%, 5 fl oz of wine at about 12%, or 1.5 fl oz of 40% spirits. NIAAA notes these may not match customary serving sizes, so use the drink builder for real pours.
How long does it take for alcohol to leave your body?
The body removes alcohol at a roughly steady pace that varies between people; only time lowers BAC. The first example above takes 3 h 40 min to reach about zero, but your real BAC may take longer, and a zero estimate does not show that you are unimpaired.
Why do women reach a higher BAC from the same drinks?
The Widmark factor r is the share of body weight that alcohol spreads into. The calculator uses the classic averages, 0.55 for women and 0.68 for men, so at the same weight the same drinks give women a higher estimate.
Sources
- NIAAA — What Is A Standard Drink?
- NHTSA — Drunk Driving (legal limits and crash risk)
- NIAAA — Understanding the Dangers of Alcohol Overdose
- eCFR — 49 CFR 382.201, Alcohol concentration (commercial drivers)
- Wisconsin Department of Justice, Crime Laboratory — Alcohol Monograph (elimination rates, time to peak)
This is a theoretical estimate for education only. It cannot determine whether you are legally or safely able to drive, operate machinery or make any other safety decision; your actual BAC may be higher. Never drive after drinking, and do not use this result as evidence in any legal matter.