Blood Alcohol Content (BAC) Calculator
Estimate blood alcohol content from drinks consumed, body weight, and time elapsed.
Cómo funciona
This calculator estimates blood alcohol content (BAC) using the Widmark formula, a long-standing method that combines total alcohol consumed, body weight, a sex-based distribution ratio, and the rate at which the body metabolizes alcohol over time.
The core formula is BAC = (alcohol consumed in grams ÷ (body weight in grams × distribution ratio)) × 100, minus the amount metabolized since drinking started (roughly 0.015% per hour for most people). The distribution ratio accounts for how alcohol spreads through body water, which differs on average between men and women (commonly modeled as about 0.68 for men and 0.55 for women) due to typical differences in body composition.
One standard drink is generally defined as containing about 14 grams (0.6 fl oz) of pure alcohol — roughly a 12 oz regular beer, a 5 oz glass of wine, or a 1.5 oz shot of 80-proof spirits — though actual alcohol content varies by beverage strength and pour size, which is the biggest source of error in any BAC estimate.
Elimination rate — the ~0.015%/hour figure — represents the average speed at which the liver metabolizes alcohol out of the bloodstream. This rate is fairly consistent for a given person but varies across individuals based on liver function, genetics, and other factors, so it's an average rather than a precise constant.
Many factors this calculator cannot account for meaningfully affect actual BAC: food in the stomach slows alcohol absorption, medications can interact with alcohol metabolism, tolerance affects impairment level at a given BAC, and individual metabolic rate varies. Two people of identical weight and sex who consume the same drinks can have meaningfully different actual BAC.
Because of these limitations, this tool is intended for educational and rough-estimate purposes only — to illustrate how the Widmark formula works and give a general sense of how drinks, weight, and time interact. It should never be used to decide whether it's safe to drive, operate machinery, or engage in any activity requiring sobriety.
The Widmark formula dates back to the 1930s and remains the basis for most simplified BAC estimation tools today, even though modern forensic toxicology uses more sophisticated models that account for additional individual variables — its enduring appeal is that it captures the dominant factors (amount consumed, body size, sex, and elapsed time) with a formula simple enough to compute by hand.
Is this accurate enough to decide if I can drive?
No — this is a rough estimate only. Actual BAC depends on many factors this calculator can't account for. Never use it to judge whether it's safe to drive.
What counts as one standard drink?
About 14 grams of pure alcohol — roughly a 12 oz regular beer, a 5 oz glass of wine, or a 1.5 oz shot of 80-proof liquor — though actual content varies by specific beverage.
Why does the calculator ask for sex?
It's used to apply a different distribution ratio (how alcohol spreads through body water), since this differs on average between men and women due to typical body composition differences.
How fast does the body eliminate alcohol?
On average, about 0.015% BAC per hour, though this varies somewhat between individuals based on liver function and other factors.
Does eating food before drinking lower my BAC?
Food slows how quickly alcohol is absorbed into the bloodstream, which can lower peak BAC and spread out its effects, but this calculator doesn't model food intake directly.
Why might two people with the same inputs have different actual BAC?
Individual differences in metabolism, tolerance, medication interactions, and absorption rate all affect actual BAC in ways a formula-based estimate can't capture.
What BAC level is considered legally impaired for driving?
This varies by jurisdiction — commonly 0.08% in many places, but always check your local legal limit, and remember impairment can begin well below any legal threshold.
Can this calculator tell me when I'm sober enough to drive?
No — it provides only a rough educational estimate. The only reliable way to ensure you're safe to drive is to not drive after drinking any amount of alcohol.
How old is the Widmark formula?
It dates back to the 1930s and remains the basis for most simplified BAC estimation tools, even though modern forensic methods use more advanced models with additional variables.
Is a BAC calculator ever used for legal or medical purposes?
No — legal and medical determinations of BAC rely on actual breath, blood, or urine testing, not formula-based estimates like this one, which are for general educational reference only.