BAC Calculator

Blood Alcohol Concentration (BAC) is a measure of the amount of alcohol in the bloodstream, typically expressed as grams of alcohol per 100 mL of blood (%). This tool uses the Widmark formula with the Forrest method adjustment, which has been adopted in medicine and forensics worldwide.

By adjusting the standard Widmark formula for height, we can estimate body water distribution more accurately. The Forrest method incorporates height (cm) alongside weight (kg), gender, and total pure alcohol consumed (grams) to calculate peak BAC. Current BAC is then estimated by subtracting the amount metabolized over time (average rate: 0.15% per hour).

Height adjustment accounts for individual differences in body composition. For example, taller individuals typically have higher body water percentages, resulting in slightly lower BAC levels for the same alcohol consumption compared to shorter individuals of equal weight.

Under Japanese traffic law, a breath alcohol level of 0.15 mg/L or more (roughly BAC ≥ 0.03%) constitutes drunk driving. Note that this tool provides statistical estimates only — actual BAC varies significantly with food intake, physical condition, drinking pace, age, metabolism, and individual health factors. Drunk driving is strictly prohibited by law.