BAC stands for Blood Alcohol Concentration. It shows the amount of alcohol in a person's bloodstream. It is expressed as a percentage, and it plays a critical role in DWI cases, traffic stops, field sobriety investigations, and license suspensions.
In the context of Texas law, a BAC of 0.08% or higher is the legal threshold for intoxication under Texas Penal Code §49.01(2). But BAC matters long before — and long after — that number.
Key Takeaways
- BAC is measured by breath, blood, or urine tests, each with unique strengths and weaknesses.
- The legal limit in Texas for DWI is 0.08%, but drivers can be arrested even below that level.
- Higher BAC levels lead to enhanced penalties, including more jail time and steeper fines.
BAC Definition
Blood Alcohol Concentration (sometimes referred to as Blood Alcohol Content) is the ratio of alcohol to blood in your body.
For example, a BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood.
BAC can be measured through:
- Breath tests (an Intoxilyzer or similar device)
- Blood tests
- Urine tests (though these are rarely used in Texas)
Courts rely heavily on BAC to determine intoxication, impairment, and penalty levels in DWI cases.
How BAC Works in the Body
Once alcohol is consumed, it enters the bloodstream through the stomach and small intestine. BAC is influenced by:
- Body weight
- Gender
- Rate of drinking
- Food consumption
- Metabolism
- Type of alcohol
- Time between drinks
Peak BAC is usually reached 30 to 90 minutes after consumption.
Legal BAC Limits in Texas
Under Texas law:
- 0.08% = Per se intoxicated (automatic DWI threshold).
- 0.15% or higher = Enhanced penalties (Class A misdemeanor).
- Commercial drivers have an even lower limit: 0.04%.
- Any detectable alcohol in minors under 21 can lead to a DUI charge.
A BAC of 0.08 is not required to be charged with DWI. If officers believe alcohol or drugs impaired your driving, they can arrest you even with a lower reading.
Three Ways BAC Is Tested
It's important to understand that you can initially refuse BAC testing. However, if you're arrested, the police will obtain a warrant, and you will be required to comply. The refusal can also lead to a suspension of your driver's license.
Texas uses three different testing methods to determine a driver's BAC:
1. Breath Tests (Most Common)
A breath test uses a machine, such as the Intoxilyzer, to measure alcohol in the deep breath you take. Breath tests are fast, easy to use on the roadside, and give immediate results. However, they are vulnerable to calibration problems, operator mistakes, temperature changes, and certain medical or digestive conditions.
Some of our senior trial attorneys recommend choosing the breath test (if you're given an option) because it's the least reliable form of chemical testing and often the easiest to challenge in court. Because breath tests measure alcohol in real time, they are also poor at detecting any potential long-term drug use.
2. Blood Tests (Most Accurate)
A blood test is performed by a medical professional who draws a blood sample for laboratory analysis. If you refuse testing, officers can obtain a warrant to take your blood. Blood tests are generally more reliable and less affected by outside factors. The main drawbacks are timing delays, the potential for contamination, and storage issues.
Personally, I recommend choosing the blood test because, in many cases, the delay between a traffic stop and the blood draw can actually benefit the defense, as BAC can rise or fall over time.
Important: Once police obtain a search warrant, don’t protest the blood draw. Your blood can (and will) be taken by force if necessary.
3. Urine Tests
Urine tests are rarely used in Texas except when officers suspect drug impairment. These tests can detect a wider range of substances, including drugs, and can show alcohol use for a longer period, sometimes up to 36 hours. However, urine testing is considered less accurate than blood sampling and carries a higher risk of contamination.
BAC and DWI Penalties
BAC directly affects the penalties of a Texas DWI case.
BAC Under 0.15%
- Class B misdemeanor
- Up to 180 days in jail
- Up to $2,000 fine
- License suspension
BAC 0.15% or Higher
- Upgraded to a Class A misdemeanor
- Up to 1 year in jail
- Up to $4,000 fine
- An ignition interlock is often required.
Higher BAC levels can also be used to justify:
- Enhanced sentencing
- Stricter probation terms
- More aggressive prosecution
Why BAC Is Not Always Accurate
BAC numbers can be flawed. Common issues include:
- Improper breath-test machine calibration
- Residual mouth alcohol
- Certain medical conditions (GERD, diabetes)
- Lab contamination during blood testing
- Delays between driving and testing
- Rising BAC (when BAC increases after the stop)
Three of our senior trial attorneys -- James Fletcher in Austin, Chris Denuna in Houston, and RC Pate in San Antonio -- are certified DWI scientists, having earned the designation of American Chemical Society Forensic Lawyer-Scientist. Five more of our attorneys are currently completing the training. To date, only 41 lawyers in Texas have earned this designation.
Our attorneys' advanced training enables us to aggressively challenge BAC evidence, which can sometimes result in a dismissal.
BAC vs. Impairment
A critical point: BAC does not always equal impairment.
Some people show signs of impairment at 0.04%. Others show none at 0.10%.
Texas law recognizes this by allowing DWI charges even with a BAC below 0.08 when there is evidence of:
- Loss of normal use of mental faculties
- Loss of normal use of physical faculties
The criteria for "impairment" can be ambiguous, and whether you're arrested depends on a split-second decision by the officer who pulls you over. An experienced DWI attorney must evaluate each case individually.\
FAQs About BAC
Is BAC the same as impairment?
No. BAC is a number. Impairment varies based on the person, health, metabolism, and timing.
How many drinks does it take to reach 0.08%?
For many adults, it will take between 2 to 4 drinks within an hour. But this varies widely based on body size and metabolism.
Can BAC rise after you stop drinking?
Yes. Your BAC can continue to climb for up to 90 minutes after your last drink, which can impact test results.
Let Us Help
At Michael & Associates, we successfully challenge — and beat — DWIs all the time. If you believe there was an issue with your testing, contact us for a free case review.
We are currently accepting clients in the following Texas counties:
- Austin area / Central Texas: Travis, Williamson, Bastrop, Bell, Caldwell, Coryell, Lampasas, Llano, Hays, Milam, Blanco
- Dallas / Fort Worth area: Dallas, Collin, Denton, Ellis, Rockwall, Tarrant
- Houston area: Harris, Galveston, Fort Bend, Montgomery, Waller, Brazoria
- San Antonio area: Atascosa, Bexar, Bandera, Comal, Gillespie, Guadalupe, Kendall, Medina, Wilson
