Blood alcohol concentration (BAC) is the share of your blood that is alcohol: 0.08% means 0.08 grams per 100 milliliters. This calculator estimates it with the Widmark formula, the method forensic toxicologists have used for a century, from the drinks you had, your body weight and sex, and the time since you started drinking.
No BAC estimate tells you it is safe to drive. Formulas cannot account for how fast you drank, what you ate, medications, or your own metabolism, and impairment starts with the first drink. If you have been drinking, do not drive.
How to use the BAC calculator
- Choose US (pounds and fluid ounces) or metric (kilograms and milliliters).
- Select your sex and enter your body weight.
- Count your beers, glasses of wine and shots at standard strengths. For anything else, such as a strong IPA or a cocktail, enter the number of drinks, the size of each and its alcohol by volume.
- Enter the hours since your first drink.
- Read the estimated BAC now, the peak it implies and the approximate time until alcohol is fully eliminated.
The Widmark formula
- A = grams of alcohol = volume (mL) × ABV × 0.789 g/mL
- W = body weight in grams
- r = Widmark distribution factor: 0.68 for men, 0.55 for women
- β = elimination rate, 0.015% per hour
- t = hours since drinking began
The first part gives the peak concentration if all the alcohol were absorbed at once; the second subtracts what the liver has cleared since.
Worked example
A woman who weighs 140 lb drinks two 5-oz glasses of 12% wine over the evening and checks two hours after her first glass:
Alcohol: 2 × 147.9 mL × 12% × 0.789 = 28.0 g (two standard drinks)
Peak: 28.0 ÷ (0.55 × 63,503 g) × 100 = 0.080%
After two hours: 0.080 − 0.015 × 2 = 0.050%. At 0.015% per hour, reaching zero takes about 3 hours 20 minutes more.
Even at 0.05%, coordination, alertness and response to hazards are measurably reduced.
What BAC levels mean
Effects described by NHTSA and NIAAA, which vary between people:
| BAC | Typical effects |
|---|---|
| 0.02% | Relaxation, some loss of judgment, harder to do two things at once |
| 0.05% | Lowered alertness and coordination, slower response to hazards |
| 0.08% | Poor muscle coordination; impaired judgment, memory and speed control |
| 0.10% | Clearly slowed reactions, slurred speech, trouble staying in a lane |
| 0.15% | Major loss of balance and muscle control; vomiting possible |
| 0.30% and up | Risk of passing out, alcohol poisoning and dangerously slowed breathing |
A BAC above about 0.30%, or someone who cannot be woken, is a medical emergency. Call 911.
Why the estimate can be wrong
- Absorption takes time. BAC usually peaks 30 to 90 minutes after the last drink, so it can still be rising when the formula assumes it is falling.
- Food slows absorption and lowers the peak; drinking on an empty stomach raises it.
- Pours are bigger than you think. A restaurant wine glass often holds 6–9 oz, and many beers are 7–9% ABV.
- People differ. Elimination rates range from about 0.010% to 0.020% per hour, and body water varies with muscle and fat.
Planning ahead
If you are hosting, the party drinks calculator helps you plan quantities, and arranging rides should be part of the plan. Alternating alcoholic drinks with water also helps; see the water intake calculator for daily fluid needs.
Informational only — not medical or legal advice. This estimate cannot be used to decide whether you can drive, operate machinery or take medication. In an emergency, call 911.
Frequently asked questions
Can this calculator tell me if I am safe to drive?
No. No BAC estimate tells you it is safe to drive. Real blood alcohol can be much higher than any formula predicts, and impairment begins well below the 0.08% legal limit. If you have been drinking, do not drive; use a designated driver, rideshare or public transit.
How fast does the body eliminate alcohol?
Most adults clear roughly 0.015% BAC per hour, with a typical range of about 0.010–0.020%. Coffee, cold showers, food after drinking and exercise do not meaningfully speed this up; only time does.
What is a standard drink in the US?
The NIAAA defines a US standard drink as 14 grams of pure alcohol: 12 fl oz of 5% beer, 5 fl oz of 12% wine or 1.5 fl oz of 40% (80-proof) spirits. Many craft beers, large wine pours and mixed drinks contain more than one standard drink.
Why do women reach a higher BAC than men from the same drinks?
On average women have a lower proportion of body water at the same weight, so alcohol is less diluted. Widmark's factor reflects this: 0.55 for women versus 0.68 for men. Differences in alcohol metabolism in the stomach also play a part.
What is the legal BAC limit?
Every US state sets 0.08% for drivers 21 and older except Utah, which uses 0.05%. Commercial drivers are limited to 0.04%, and drivers under 21 face zero-tolerance limits. You can be charged with impaired driving below these levels.