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Waiting to Get Behind the Wheel: Why Experts Can’t Agree on BAC Calculators

Posted by Christopher Martens | Jul 11, 2018 | 0 Comments

Calculating BAC

Blood alcohol concentration or content (BAC) is a critical legal element in DUI cases. Many assume BAC defines DUI in California statute, and indeed it plays a significant role. Unfortunately, breathalyzer devices can be inaccurate, and there is no sure-fire way to accurately calculate your BAC without a professional grade device or a blood draw. Even just using one of the many BAC calculator apps can leave you with—at best—an estimate. And when it comes down to fractions of a percent making the difference between being guilty or not guilty, estimates aren't good enough.

Experts can't agree on BAC calculators and suggest science still has a way to go before we can accurately and consistently calculate BAC. Importantly, it's essential for people to be able to accurately calculate their BAC after drinking so they can judge for themselves how long they should wait before driving. Having a foolproof method of doing so would help reduce drunk driving fatalities statewide.

Getting a Rough Estimate

But if experts can't agree, where does that leave us? The best rule of thumb to avoid a DUI conviction is, of course, to never drive after drinking. But if you're wondering how long before you are legally “sober” after drinking, you may have to do some math and make a guess. Let's review the factors that can affect BAC.

The Influencing Factors

The typical BAC calculator asks for your gender, weight, number of drinks you've had, and how long you've been drinking. These simple factors can produce a rough estimate of where your BAC might be. But beyond that, the real science starts to get complicated. Scientists agree these factors do influence your BAC, but many other factors can complicate your efforts to arrive at an accurate number. For example, your body composition (muscle/fat ratio) can play a role in how quickly your body metabolizes alcohol. 

Similarly, while gender plays a role, the underlying factor is your body composition, and men and women typically differ in this respect. Everybody is different, and no calculator can account for the varying body compositions of each user. This is one strong reason why experts agree BAC calculators aren't as accurate as they claim.

Also, many factors can affect how quickly alcohol enters your bloodstream. For example, the contents of your stomach can slow or speed alcohol absorption. The specific foods you've eaten, down the way the food was prepared, can affect absorption rates.

Beyond biology, the type of drink you had matters immensely. All alcohol has different alcohol percentages or proofs. Most beers fall into the range of 3% to 7%. But even within this range, the effects you feel after drinking them will vary widely. And when it comes to mixed drinks, it's nearly impossible to get an accurate assessment of how much alcohol you've consumed unless you make the drink yourself. Every bartender and every establishment can have different practices when making drinks. A mixed cocktail at one bar may contain more alcohol than the same type of drink at another.

Not Reliable Enough

Given these variations, it's easy to see why experts urge people to not rely on BAC calculators before getting behind the wheel. Handheld BAC devices, such as BAC key chains, are a step up in terms of accuracy, but many do not operate the same way professional-grade devices law enforcement use do. Professional breathalyzers are much more accurate as they involve more advanced technology (and thus cost significantly more). Unfortunately, you cannot rely on any one method alone of calculating your BAC after drinking. The legal BAC threshold in California is .08%. But you can still be charged with DUI if your BAC falls below that level if you are impaired while driving, leaving you with few tools to judge when you are legally OK to drive with any level of precision.

Fight Your DUI Charges

The good news is given all the complications and shortcomings of BAC science DUI cases are not impossible to beat. Even if your BAC was above .08%, a skilled attorney may be able to challenge your BAC test results. It takes a clear understanding of BAC science as well as the particulars of your case, but many attorneys have obtained complete dismissals for their clients by challenging the breathalyzer test results alone.

Call a California DUI defense attorney if you are facing DUI charges. No matter your BAC, an attorney can help you understand your options for fighting your charges and the defenses you may be able to leverage.

Facing DUI charges can be overwhelming, but experienced Visalia area DUI defense attorney Christopher Martens can help you face your charges with confidence. At The Law Offices of Christopher Martens, we can help you navigate the criminal prosecution process from start to finish and are not afraid to take your case all the way to trial. Martens has practiced criminal defense for over ten years and knows how to defend your rights.  Contact our Visalia or Hanford offices at 559-967-7386 or email us at [email protected] to discuss a possible plan of action for your case.

About the Author

Christopher Martens

Bio Visalia and Bakersfield criminal defense attorney who has dedicated his life to helping those who have been accused of crimes or injured due to the negligence of others.


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