Blood Alcohol Content (BAC) Calculator

This calculator uses the Widmark formula, which estimates BAC by dividing the total grams of alcohol consumed by the product of body weight in kilograms and a gender-specific factor (0.68 for males and 0.55 for females). The result is then multiplied by 100 to express BAC as a percentage. This method provides an approximation and does not account for factors like metabolism, medications, or drinking duration.

The gender factor reflects physiological differences in body water composition. On average, males have a higher percentage of body water (about 68%) compared to females (about 55%), which dilutes alcohol more effectively. This means that, for the same amount of alcohol consumed, females typically reach a higher BAC than males of the same weight.

In many countries, the legal driving limit is 0.08% BAC. However, some regions enforce stricter limits, such as 0.05% in Australia and parts of Europe, or even 0.02% for novice or commercial drivers. It's important to check your local laws, as impairment can occur at levels below the legal limit, and zero-tolerance policies may apply in some areas.

Several factors can influence actual BAC levels, including the rate of alcohol absorption (affected by food intake), individual metabolic rates, medications, health conditions, and the time elapsed since drinking. This calculator provides an estimate but cannot account for these variables, so results should be used cautiously.

A common misconception is that higher alcohol tolerance lowers BAC. In reality, tolerance affects how you feel but does not change your BAC level. You may feel less impaired, but your BAC remains the same, and you can still face legal or safety risks. Another misconception is that drinking coffee or taking a cold shower reduces BAC—it does not; only time allows your body to metabolize alcohol.

This calculator can help you estimate your BAC and understand when it might be unsafe to drive. For example, if your calculated BAC approaches or exceeds the legal limit, you should arrange alternative transportation. Additionally, consider the time it takes for your body to metabolize alcohol—on average, about 0.015% BAC per hour—and plan accordingly to avoid driving under the influence.

Body weight affects BAC because alcohol is distributed throughout the body’s water content. A person with higher body weight typically has more water volume, which dilutes alcohol more effectively, resulting in a lower BAC for the same amount of alcohol consumed. This is why body weight is a critical factor in BAC calculations.

While a BAC calculator provides a helpful estimate, it cannot account for real-time factors like alcohol absorption rates, individual metabolism, or the cumulative effects of multiple drinks over time. Additionally, impairment varies by individual and can occur at BAC levels below the legal limit. Always prioritize safety and avoid driving if you’ve consumed alcohol, regardless of your calculated BAC.