Understand how alcohol is processed. This free blood alcohol calculator gives a rough educational BAC estimate from your weight, drinks and time – it cannot tell you if you’re safe to drive, and the only safe amount before driving is zero.
A “standard drink” is about 14 g of pure alcohol (a 12 oz beer, 5 oz wine or 1.5 oz spirits).
BAC varies with food, metabolism, medication, health and more – no formula is reliable for an individual. Legal limits differ by region and many are well below the figures shown. Never rely on this to drive.
How Blood Alcohol (BAC) Calculator Works
This tool gives a rough, educational estimate of blood alcohol concentration using a version of the Widmark equation, based on body weight, standard drinks, sex, and time elapsed. It is not a breathalyzer reading and cannot tell you whether you are safe or legal to drive.
Formula: Alcohol (g) = Standard drinks × 14. BAC (%) = (Alcohol (g) ÷ (Body weight (g) × r)) × 100. Then subtract 0.015 × Hours elapsed from that number, down to a minimum of 0. The distribution ratio r is 0.68 for males and 0.55 for females.
- Sex — male or female, used to select the Widmark distribution ratio (r = 0.68 or 0.55)
- Body weight — entered in kg or lb; lb is converted to kg (× 0.45359237) before the formula runs
- Standard drinks — the number of standard drinks, each treated as 14 g of pure alcohol
- Hours since first drink — used to subtract 0.015% BAC per hour for the body’s estimated elimination rate
Example Scenarios
| Sex | Weight | Drinks | Hours elapsed | Estimated BAC |
|---|---|---|---|---|
| Male | 80 kg | 1 | 1 | 0.011% |
| Male | 75 kg | 3 | 2 | 0.052% |
| Female | 60 kg | 2 | 1 | 0.070% |
| Female | 65 kg | 5 | 4 | 0.136% |
| Male | 70 kg | 8 | 1 | 0.220% |
Blood Alcohol (BAC) Calculator FAQ
Can I use this calculator to decide if I’m safe to drive?
No — never use it for that. Real BAC depends on food, metabolism, medication, hydration, and other factors this formula cannot capture, and the only truly safe amount of alcohol before driving is zero. This tool is for general education only.What formula does this calculator use?
It uses a version of the Widmark equation: alcohol grams divided by body weight in grams times a distribution ratio, multiplied by 100, minus 0.015% for every hour elapsed since the first drink. It’s a simplified academic model, not a clinical measurement.Why do male and female results differ for the same weight and number of drinks?
The calculator applies a different distribution ratio (0.68 for males, 0.55 for females) because average body water percentage differs by sex, and alcohol distributes through body water. This is a population average, not an individual measurement.What counts as one “standard drink” in this calculator?
Each standard drink is treated as about 14 grams of pure alcohol — roughly a 12 oz beer, a 5 oz glass of wine, or 1.5 oz of spirits. Stronger or larger pours contain more alcohol than one standard drink.Does the estimate account for food, medication, or how fast I drank?
No. The formula only uses weight, sex, drink count, and elapsed time. Eating beforehand, medications, drinking speed, sleep, and overall health can all change actual BAC in ways this simplified calculator cannot capture.Is my estimated BAC the same as my region’s legal driving limit?
Not necessarily. Legal limits vary by country and state, and many are set well below what a simple formula like this can reliably estimate for any one person. Never compare this estimate to a legal limit to judge whether it’s okay to drive.Related Calculators
To think about alcohol from other angles, try the alcohol units calculator to see how a drink’s size and strength add up, the alcohol calorie calculator to check how drinks fit into your daily calories, or the sobriety calculator to track time since your last drink.