BAC Calculator
Calculate Blood Alcohol Concentration
About the BAC Calculator
Blood alcohol concentration estimates how much alcohol is in your bloodstream, expressed as a percentage. This calculator uses the well-established Widmark formula, factoring in your sex, body weight, the number of standard drinks, and the time elapsed since you started drinking, and flags when the estimate crosses the common 0.08% legal driving limit.
People use it to understand how drinks accumulate and how slowly alcohol clears — useful for planning a night out or appreciating why "just a couple" can still register hours later. It is strictly an educational estimate: individual metabolism, food, medication, and many other factors mean your true BAC can differ significantly, and no calculator can tell you it is safe to drive.
How to Use the BAC Calculator
- Select your sex (it sets the body-water distribution constant in the formula).
- Provide your body weight in kilograms.
- Enter the number of standard drinks consumed (each counted as 14 grams of alcohol).
- Enter the hours elapsed since you began drinking.
- Read your estimated BAC, with a warning shown if it is at or above 0.08%.
Why Use ToolForge’s BAC Calculator
- It uses the Widmark method with sex-specific distribution constants (0.68 for men, 0.55 for women), the standard scientific approach to estimating BAC.
- It accounts for elimination over time, subtracting roughly 0.015% per hour, so it reflects how alcohol clears rather than just how much you drank.
- It defines a drink as 14 grams of pure alcohol, the standard-drink convention, so counts are consistent.
- It runs entirely in your browser — nothing about your drinking is uploaded.
Frequently Asked Questions
How accurate is this BAC estimate?
It is an approximation. The Widmark formula uses population averages and cannot account for your individual metabolism, food in your stomach, medications, hydration, or health conditions. Your actual BAC may be higher or lower, so never treat the result as a green light to drive.
What counts as one standard drink?
This calculator uses the common standard of 14 grams of pure alcohol per drink — roughly a 12 oz regular beer, a 5 oz glass of wine, or a 1.5 oz shot of spirits. Stronger or larger servings count as more than one drink.
How long does it take for BAC to return to zero?
Alcohol leaves the bloodstream at roughly 0.015% per hour, and that rate cannot be sped up by coffee, water, or food. Depending on how much you drank, it can take many hours to reach zero, which is why a BAC can still be significant the morning after.
Is it safe to drive below 0.08%?
Not necessarily. Impairment begins well before 0.08%, the limit is lower in many places and for commercial or young drivers, and any amount of alcohol can affect reaction time. This tool is educational only and is not a measure of fitness to drive.
