Blood Alcohol Content (BAC) Calculator — Free Online BAC EstimatorWidmark Formula · BAC by weight · drinks · time elapsed
Use this free Blood Alcohol Content (BAC) Calculator to estimate your blood alcohol level based on key personal variables including body weight, biological sex, number of standard drinks consumed, alcohol percentage (ABV), and time elapsed since first drink.. To better understand how your body processes energy and metabolism alongside alcohol intake, you can also calculate your basal metabolic rate (BMR). This online BAC estimator applies the industry-standard Widmark BAC formula — the same blood alcohol calculation method referenced in forensic toxicology, DUI law enforcement, and clinical alcohol research — to give you an estimated BAC percentage reading in grams of alcohol per 100ml of blood (g/dL). ⚠ Important Disclaimer: This BAC calculator is intended strictly for educational and informational purposes only. Individual alcohol metabolism rates vary significantly based on liver function, food intake, hydration, medications, and tolerance. This tool must NEVER be used to determine fitness to drive, operate machinery, or establish legal responsibility — drink driving laws set legal BAC limits (typically 0.08% in the US, 0.05% in Australia and Europe, and 0.00% for new drivers in many countries) that only certified breathalyzer or blood tests can legally confirm. Always drink responsibly and never drive after consuming alcohol.
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Blood Alcohol Calculator — Estimate BAC and Time to Sober With Widmark Formula
Blood Alcohol Concentration (BAC) is the mass of alcohol per volume of blood, expressed as grams per 100 mL (g/dL). The Widmark formula estimates BAC: BAC = (alcohol consumed in grams) / (body weight × distribution factor) - (elimination rate × hours). For a 70 kg male (distribution factor 0.68) consuming 3 standard drinks (42g alcohol) in 2 hours: BAC ≈ 42/(70×0.68) - (0.015×2) = 0.882/47.6 - 0.03 = 0.0585 g/dL (0.058%). The legal driving limit in most US states is 0.08%. The BAC calculator makes this estimate but prominently notes it is an estimate, not a measurement.
The distribution factor differs significantly by sex: approximately 0.68 for men and 0.55 for women, reflecting that women have a higher proportion of body fat (which does not absorb alcohol) relative to water-rich lean tissue. The same amount of alcohol in a woman of equal body weight produces roughly 20-30% higher BAC than in a man. Food slows alcohol absorption but does not change the total alcohol absorbed — it only shifts the peak BAC time by 1-2 hours and reduces the peak magnitude by 10-35% depending on meal composition and timing.
Alcohol elimination averages 0.015-0.020 g/dL per hour (approximately one standard drink per hour) and cannot be accelerated by coffee, food, exercise, or time-based interventions other than waiting. A person reaching BAC 0.15% needs at least 7-10 hours to reach 0.00% — meaning someone drinking heavily at 11 PM may still have measurable BAC well past 8 AM. The calculator projects the time at which BAC returns to zero so the "sleep it off" timeline is based on physiology rather than wishful thinking.