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​BAC Calculators: Are They Accurate?

There’s no doubt that drunk driving remains a serious problem across the country. Still, those accused of drunk driving and subject to various tests, such as Breathalyzers and blood alcohol concentration (BAC) levels, have legal rights. Not every person charged with drunk driving is actually driving while under the influence or has an illegal amount of alcohol in their system.

In addition, law enforcement officers often mishandled these cases, giving more rights to those accused of a DUI. Therefore, anyone facing drunk driving charges, no matter where they live, should reach out to a seasoned DUI defense attorney for help right away.

How Accurate are BAC Calculators?

Various free and readily available blood alcohol content (BAC) charts and calculators can guide drivers in approximating their current BAC levels. However, it’s crucial to understand that these charts and calculators have inherent limitations. They typically come with lengthy disclaimers or even warnings concerning their accuracy. This is because multiple factors stand to affect your BAC that are not considerations in chart and calculator BAC estimates.

Most online BAC calculators use the Widmark equation to estimate a BAC. This equation is known to have an average uncertainty of around 20 percent, meaning that any estimate made by a BAC calculator can be up to 20 percent too high or too low.

Drivers need to understand that these tools can only provide an approximation of their BAC. They should never rely on them to determine whether or not it’s safe to drive.

BAC Calculator and Chart Assumptions

Serving Size

Most charts and calculators have predefined values for both alcohol serving size and alcohol content.

For example:

  • A serving of beer is 12 ounces and has a 4.5 percent alcohol content
  • A glass of wine equals 4 ounces and contains 15 percent alcohol content
  • A shot of straight liquor is 1.5 ounces and has a 40 percent alcohol content

If you consume a drink with a larger serving size or one stronger than average, the calculator will underestimate your actual BAC.


BAC calculators don’t consider the amount of food in your stomach or that you might consume while you drink. BAC rises faster when you consume alcohol on an empty stomach because food typically slows the absorption of the alcohol.


BAC calculators assume your alcohol consumption rate is consistent over a specified period of time. For example, if you consume drinks more quickly than “one standard drink per hour,” your estimated BAC will be miscalculated.


BAC calculators rely on a formula based on average values such as:

  • The average amount of water in the body
  • The average amount of water content in the blood
  • The average metabolism rate

Individual factors impacting these values aren’t part of the calculations and, therefore, may contribute to inaccurate estimations.


Some over-the-counter and prescription medications can change the effects of alcohol. For example, they allow alcohol to be absorbed at different rates, which can have a more significant effect on the alcohol-consuming individual.

While charts and interactive BAC calculators and estimators can come in handy for providing a rough idea of someone’s intoxication, NEVER rely on them for determining if you should get behind the wheel after drinking—no matter how little you think you’ve had. It’s not worth the risk to your freedom and legal record.

If you need to use a BAC chart or calculator, you most likely shouldn’t get behind the wheel anyway. You can avoid legal problems by using a designated driver, using a rideshare service, staying where you are, or taking the bus.

What Happens if You Face DUI Charges?

Suppose you are stopped by a law enforcement agent while intoxicated. In that case, you will be handcuffed and taken to the police station. Officers will likely search and tow your car, and you will have to pay for it. The law enforcement officer will request that you submit to a Breathalyzer test. In most states, if you refuse, your driver’s license will automatically be suspended for one year.

If the test results reveal that your blood alcohol level (BAC) is 0.8 percent or higher, you can receive a driver’s license suspension. You will go before a judge who will set your bail. Before you can get released from jail, you might have to post bail. This bail guarantees you will return for your court sentencing date. The sooner in this process that you can reach out to a DUI defense lawyer, the better.

DUI Penalties

A DUI charge can come with strict consequences, even if you have never faced criminal charges in the past.

If this is not your first DUI charge, your consequences will be even more severe than those of a first-time offender, which, depending on where your arrest occurred, can include:

  • Court costs and fees
  • A jail sentence
  • Fines
  • A license suspension
  • Probation
  • Required enrollment in a substance abuse education course that you will pay for
  • Attendance at a victim impact panel
  • Mandatory urine testing for drugs and alcohol
  • Other terms of probation

These are only the legal consequences, as there will be additional impacts on your life, such as damage to your reputation, employment issues both now and in the future, and family problems. While a DUI defense lawyer might not help with some of these issues, reducing your charges and penalties will certainly help.

Potential DWI/DUI Defenses

Experienced DUI Defense Lawyer for drunk driving charges in Denver areaEvery DWI/DUI case is unique and deserves the attention of a legal professional. There is no single right way to fight back against a DWI charge. A careful evaluation of the individual details in the case will highlight which defense strategy may be most effective. A highly successful defense in one case can fail miserably in another.

You need an attorney who refuses to offer cookie-cutter solutions to any criminal charges, especially those as serious as DWI/DUI charges. They should evaluate your case on its own merit, investigating the situation from beginning to end and looking especially at areas where law enforcement may not have done their job correctly or legally.

Depending on your case, your DUI defense lawyer might use one or more of the following defenses to have your charges decreased, dropped, or have you found not guilty in court:


Lack of Physical Control of the Vehicle Defense

You weren’t actually driving, operating, or in physical control of the car: You must be driving or in physical control of a vehicle to be found guilty of driving while impaired (DWI or DUI) in this state.

But what does that really mean? While driving is pretty much self-explanatory, what is physical control? Interestingly, neither the legislature nor the courts have defined physical control in many states.

Even still, law enforcement officers often allege that you’re in physical control of the vehicle if you are:

  • Sleeping in the driver’s seat of the vehicle with the keys either in the ignition or in your pocket
  • In the vehicle’s passenger seat with the keys in your pocket
  • Standing near the vehicle with the keys in your pocket

While the police officers might purport that you were in physical control of the vehicle at a given point in time, that doesn’t mean you really were. If you want to raise this physical control defense, hiring a seasoned DUI defense attorney is in your best interests. Your attorney will need to subpoena witnesses who can testify on your behalf. They will also need to conduct a proper questioning of both the prosecutor’s witnesses and your witnesses.

The Right to Defense Counsel

In every state, including those with motorcycle laws, law enforcement officers must read an Implied Consent Advisory to all motorists before they submit to chemical testing. Under this legal advisory, officers should first ask drivers if they want to contact an attorney for advice on testing before the officer conducts testing.

If a driver tells the officer that they want to speak to an attorney, the officer must give them access to a phone in a reasonable time to contact an attorney.

Reasonable time depends on:

  • The time of the day the traffic stop occurred
  • The diligence the driver showed in their attempt to reach a lawyer

Suppose the driver did not get a reasonable amount of time to successfully reach a defense attorney. In that case, their DUI defense lawyer might successfully have the charges dropped entirely.

Post-Driving Consumption Defense

This defense says that any alcohol you consumed was drunk after you last drove a vehicle. It is important to collect evidence after a drunk driving accident to determine whether the driver was truly intoxicated at the time of the incident. In this case, the suspect admits they drove a vehicle and were drunk when the officer had them take a test. However, the key to this defense is that they weren’t intoxicated while driving the car. Essentially, this defense alleges that the driver drove before drinking. Of course, this defense won’t work for every DWI charge, but it has proven successful in some.

Dishonored Second Test Request Defense

The law enforcement officers did not properly and legally honor the suspect’s request for a second test. Under some state laws, all motorists requested to take either a blood, breath, or urine alcohol test have a right to request a second test.

For example, if a law enforcement officer asks a driver to take a breath test, the driver can consent to take a breath test but also request a blood test. Under some state laws, a private company must perform a blood test. If the motorist requests a second test, the police must give the motorist access to a telephone, so they can contact a private testing company.

If the police don’t honor this right after a driver requests a second test, then the court must suppress the original test taken by the police. Without the initial test, there’s no DWI case, and the charges might be dropped.

Save your freedom, job, and everything else you hold dear by hiring an aggressive, experienced DUI defense lawyer to help you raise these and other DWI defenses.

Other Defenses for DUI Charges

When you hire a skilled DUI defense lawyer, they will examine all the details and circumstances in your case. They will identify the best defense for your charges based on their findings.

Potential defenses might include:

  • The police officer lacked probable cause to pull you over or to request that you submit to a BAC test
  • The police officer didn’t administer the field sobriety test in exact accordance with the proper standard
  • The police officer didn’t score your sobriety test correctly
  • You have an illness or physical condition with symptoms that might appear to be alcohol or drug impairment
  • The officer did not have the proper training to administer the Intoxilyzer test you took
  • The Breathalyzer device wasn’t properly maintained or calibrated
  • Chain of custody errors exist for your BAC blood or urine test
  • Your BAC wasn’t as high at the time of the traffic stop as it was later after some time passed
  • You were driving out of dire necessity to prevent more significant harm. For example, you rushed a person suffering a heart attack to the emergency room after drinking.
  • You drove under duress and involuntarily
  • Entrapment by the arresting officer

Contact an Experienced DUI Defense Attorney Today

You don’t have time to waste if you are facing charges of DUI. Contact an experienced DUI defense attorney today. Your criminal defense attorney in Denver will review your case thoroughly, examining every possible defense to provide you with the best outcome possible in your case.

Lauren Varner, Personal Injury Attorney

Lauren is a Personal Injury Attorney. She is Colorado native who became involved with the field of personal injury long before she became an attorney. Lauren’s professional philosophy centers around good old fashioned hard work, producing quality work product, and treating others professionally, with dignity and respect at all times.

Awards and as featured on

National Trial Lawyers Top 40 Under 40 Included in TOP 40 Under 40 by The National TRIAL Lawyers in Centennial CO Varner Faddis Top Lawyers Denver Badge – 5280 Magazine American Institute of Personal Injury Attorneys 10 Best Attorney Top 40 Under 40 5280 Denver Top Lawyers