A variety of free and readily available blood alcohol content (BAC) calculators and charts can help you approximate your BAC levels. But simplicity is not always a virtue. BAC calculators and charts have inherent limitations, and are usually accompanied by lengthy disclaimers. Some even include warnings regarding their accuracy. That’s because many factors that can affect your BAC are not considered in BAC calculator and chart estimates.It’s important to understand that BAC calculators and charts can only provide an approximation of your BAC. You should never rely on them to determine whether or not it’s safe to drive.
Assumptions that Go Off the Charts
- Serving Size – The majority of BAC calculators and charts have predefined values for both alcohol serving size and alcohol content. For instance, a beer is 12 oz. and 4.5% alcohol content, a glass of wine is 4 oz. and 15% alcohol content, and a shot is 1.5 oz. and 40% alcohol content. If you consume a drink with a larger serving size and/or one that’s stronger than average, the calculator will underestimate your BAC.
- Food – BAC calculators do not factor the amount of food in your stomach. Your BAC will rise faster when you consume alcohol on an empty stomach because there’s no food to slow the absorption of alcohol.
- Time – BAC calculators assume your alcohol consumption rate is consistent over a specified period of time. If you consume drinks more quickly than “one standard drink per hour,” your estimated BAC will be miscalculated.
- Averages – BAC calculators use a formula based on average values such as the average amount of water in the body and in the blood, and the average metabolism rate. Individual factors that affect these values are not calculated, and therefore contribute to erroneous estimations.
Online BAC Calculators
Interactive online BAC calculators can quickly give you a rough idea of your BAC level, and even your degree of impairment. Most require you to enter four data points: weight, gender, the number of drinks consumed, and the amount of time you have been drinking. Once the data is submitted, a formula is used to calculate your BAC.
It’s important to understand that BAC calculators and charts can only provide an approximation of your BAC. You should never rely on them to determine whether or not it’s safe to drive.
The accuracy and reliability of online BAC calculators are usually disclaimed in very strong terms. Rightfully, the disclaimers note that personal factors such as metabolism, health, medications, and recent consumption of food can not be taken into account. Without considering these factors, though, these tools are almost useless.
BAC Chart
BAC charts (or “alcohol impairment charts”) are also widely available. They are easy to follow and provide much of the same information offered by online BAC calculators.
Source: California Dept. of Motor Vehicles (www.dmv.ca.gov)
Here, too, the influence of personal variables make the BAC chart an inaccurate reference.