Blood Alcohol Content Calculator
Estimate your BAC from drinks, weight and time.
Each ≈ 14 g of pure alcohol.
Results update as you type.
This calculator provides estimates based on population research. Results are not medical advice. Consult a qualified healthcare provider before making health or nutrition decisions.
How it works
Blood alcohol content is the percentage of alcohol in your bloodstream, and it is the measure police, doctors and the law use to gauge intoxication. A blood alcohol content calculator estimates that figure from how much you have drunk, your body weight, your sex and how long has passed since you started drinking. It applies the Widmark formula, devised by Swedish chemist Erik Widmark in the 1930s and still the foundation of forensic alcohol calculations today. The method rests on the fact that alcohol spreads through the body's water, so a heavier person and, on average, a man dilute the same amount of alcohol into a larger volume and reach a lower peak. Each standard drink contributes about 14 grams of pure alcohol, and the body then clears it at a roughly steady rate near 0.015 percent per hour regardless of what you do. This blood alcohol content calculator subtracts that elimination over the hours elapsed to approximate your current level. People use it to understand roughly how alcohol affects them and how long it lingers, but the output is only an estimate. Real BAC depends on food, hydration, medications, drinking speed, liver health and individual variation that no formula captures. Crucially, never rely on a blood alcohol content calculator to decide whether it is safe or legal to drive; if you have been drinking, do not drive, and arrange another way home.
BAC = (grams ÷ (weight_g × r)) × 100 − 0.015 × hours; r = 0.68 male, 0.55 female
Widmark's method divides the grams of alcohol consumed by the body's water volume, approximated as body mass times a distribution ratio, which is about 0.68 for men and 0.55 for women reflecting typical differences in body water. Multiplying by 100 converts to a percentage. The body then eliminates alcohol at a near-constant 0.015 percent per hour, so that amount is subtracted for every hour that has passed since drinking began.
Source:Standard health guidance
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter standard drinks, body weight, hours since first drink and sex.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Estimated BAC updates instantly as you type — no button to press.
Frequently asked questions
How accurate is a BAC calculator?
It gives a rough estimate, not a precise reading. The Widmark formula ignores factors that strongly affect real blood alcohol, including food in your stomach, drinking speed, hydration, medications, liver function and individual metabolism. Two people with identical inputs can test quite differently. Only a breathalyser or blood test measures actual BAC. Treat any calculator result as a general guide to how alcohol may affect you, never as proof you are under a legal limit.
What counts as one standard drink?
A standard drink contains about 14 grams of pure alcohol, which is the amount in roughly 350 ml of regular beer at 5 percent, 150 ml of wine at 12 percent, or 45 ml of spirits at 40 percent. Definitions vary slightly by country, and many real-world pours, especially wine and cocktails, are larger than one standard drink, so it is easy to underestimate how many you have actually consumed.
How long does it take for alcohol to leave your system?
The body eliminates alcohol at a fairly steady rate of about one standard drink per hour, or roughly 0.015 percent BAC per hour, and almost nothing speeds this up. Coffee, cold showers, food and water do not sober you faster; only time does. So a peak BAC of 0.08 percent takes over five hours to return to zero. This is why alcohol can still be present the morning after heavy drinking.
Can I use this to decide if I can drive?
No, absolutely not. This calculator is for general awareness only and must never be used to judge whether you are fit or legal to drive. The estimate can easily be lower than your true BAC, and legal limits and impairment vary. The only safe rule after drinking is not to drive at all. Plan ahead with a designated driver, a taxi, public transport or a ride service instead.
Why do men and women process alcohol differently?
On average, women have a higher proportion of body fat and less body water than men of the same weight, so alcohol distributes into a smaller volume and reaches a higher concentration. Women also tend to have lower levels of the stomach enzyme that begins breaking down alcohol. The Widmark formula reflects this with a lower distribution ratio for women, which is why the same drinks can produce a higher BAC in a woman than a man of equal weight.