Blood Alcohol Concentration (BAC) Calculator
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This BAC calculator gives a rough estimate of your blood alcohol concentration using the Widmark formula, based on what you drank, your body weight, your sex and how long ago you started drinking.
Blood alcohol concentration (BAC) is the amount of alcohol in the bloodstream, expressed as a percentage. A BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood, the legal driving limit for adults in every US state except Utah, where it is 0.05%. Commercial drivers are held to 0.04%, and drivers under 21 face zero-tolerance laws.
The calculator uses the Widmark formula, which divides the grams of alcohol consumed by body weight times a distribution factor that reflects how much of the body is water, then subtracts the alcohol cleared since drinking began. Women typically reach a higher BAC than men after the same amount because they tend to have less body water. The result is an average estimate, not a measurement, and it can be off by a wide margin.
Alcohol and health
Alcohol is absorbed quickly from the stomach and small intestine and spreads through body water. Food in the stomach slows absorption and lowers the peak, while carbonated drinks and drinking on an empty stomach speed it up. The liver removes alcohol at a fairly steady rate, on average about one standard drink an hour, which lowers BAC by roughly 0.015% per hour. Nothing speeds this up: coffee, cold showers and exercise may make someone feel more alert but do not reduce BAC.
In the United States a standard drink contains about 14 grams of pure alcohol. That is the amount in 12 ounces of regular beer at 5% alcohol, 5 ounces of wine at 12%, or 1.5 ounces of 80-proof (40%) spirits. Many real servings are larger: a pint of strong craft beer or a generous glass of wine can contain two standard drinks.
The Dietary Guidelines for Americans advise adults who choose to drink to limit intake to two drinks or fewer a day for men and one drink or fewer for women, and note that drinking less is better for health than drinking more. Some people should not drink at all, including those who are pregnant or might be, people under 21, people taking medications that interact with alcohol, and those recovering from alcohol use disorder. The US Surgeon General and the World Health Organization have highlighted that alcohol causes several cancers, including cancers of the mouth, throat, esophagus, liver, colon and breast, and that risk rises with the amount consumed.
Excessive drinking is a leading preventable cause of death in the US; the CDC estimates it causes about 178,000 deaths a year. Short-term risks include car crashes, falls, drowning, violence, risky sexual behavior and alcohol poisoning. Long-term heavy drinking raises the risk of high blood pressure, heart disease, stroke, liver disease, digestive problems, depression, memory problems and dependence. Binge drinking, a pattern that brings BAC to 0.08% or higher, usually about five or more drinks for men or four or more for women within roughly two hours, is especially dangerous.
Alcohol poisoning is a medical emergency. Signs include confusion, vomiting, seizures, slow or irregular breathing, pale or bluish skin, low body temperature and being impossible to wake. Call 911 and do not leave the person alone; lay them on their side to reduce the risk of choking. If you are worried about your drinking, the SAMHSA National Helpline at 1-800-662-4357 is free, confidential and available around the clock.
Effects by blood alcohol concentration
Alcohol affects people differently, and tolerance can hide impairment without reducing it. The table summarizes typical effects at different BAC levels, drawing on information from the National Highway Traffic Safety Administration and the National Institute on Alcohol Abuse and Alcoholism. Driving skills decline measurably even at low levels, well before a person feels drunk, and the risk of a fatal crash rises steeply as BAC climbs.
| BAC | Typical effects | Effect on driving |
|---|---|---|
| 0.02% | Relaxation, slight warmth, some loss of judgment | Reduced ability to track moving objects and to do two tasks at once |
| 0.05% | Lowered alertness, exaggerated behavior, released inhibitions | Reduced coordination, slower response to emergencies, difficulty steering |
| 0.08% | Poorer muscle coordination, impaired reasoning, self-control and memory | Weaker concentration, speed control and hazard detection |
| 0.10% | Clearly slower reactions, slurred speech, poor coordination | Reduced ability to stay in lane and brake when needed |
| 0.15% | Far less muscle control, major loss of balance, possible vomiting | Substantial impairment of vehicle control and attention |
| 0.16–0.30% | Confusion, stupor, memory blackouts | Unable to drive safely in any sense |
| 0.31% and above | Risk of loss of consciousness, suppressed breathing and heart rate, death | — |
BAC (%) = [A ÷ (r × W)] × 100 − β × t
- A
- grams of alcohol consumed (volume × ABV × 0.789 g/ml)
- W
- body weight in grams
- r
- Widmark factor: 0.68 for men, 0.55 for women
- β
- elimination rate, about 0.015% per hour
- t
- hours since the first drink
Frequently asked questions
How accurate is a BAC calculator?
Only roughly. It uses average values for body water and alcohol elimination. Food, drinking speed, medications and individual metabolism can change real BAC considerably, so never rely on it to decide whether to drive.
How long does it take for alcohol to leave the body?
On average the body clears about 0.015% BAC per hour, roughly one standard drink an hour. Coffee, water or exercise do not speed this up.
What is a standard drink?
In the US, about 14 grams of pure alcohol: 12 oz of 5% beer, 5 oz of 12% wine or 1.5 oz of 40% spirits.
Why do women reach a higher BAC?
Women generally have less body water than men of the same weight, so the same amount of alcohol is more concentrated in the blood.
What is the legal BAC limit for driving?
0.08% for adults in all US states except Utah, which uses 0.05%. Commercial drivers are limited to 0.04%, and drivers under 21 face zero-tolerance limits.
What is the formula for BAC?
The Widmark formula: BAC (%) = grams of alcohol ÷ (body weight in grams × r) × 100 − 0.015 × hours since the first drink, where r is 0.68 for men and 0.55 for women. A 180-pound (81,600 g) man who has four US standard drinks (56 g) over two hours gets 56 ÷ (81,600 × 0.68) × 100 − 0.03 ≈ 0.071%. A woman of the same weight comes out near 0.095%, because of the smaller r.
Results are estimates for educational purposes and are not medical advice. Talk to a doctor or other qualified health professional about your situation.
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