Blood Alcohol Concentration (BAC) refers to the percentage of alcohol in a person’s bloodstream and is a critical factor in California DUI cases. If you are asking “what does BAC stand for?” or researching the BAC meaning in driving, understanding the legal BAC in California and how police measure BAC during a DUI arrest can significantly impact your defense strategy. Even a small difference in BAC results can change the severity of charges and penalties.
Key Takeaway: In California, a BAC of 0.08% or higher is illegal for most adult drivers, but you can still be charged with DUI even below 0.08% if law enforcement claims you were impaired.
Last Updated: February 2026
What is BAC? Blood Alcohol Concentration
What is BAC, What Does BAC Stand For, and What Is a High BAC for DUI in California | OC Drunk Driving Defense Attorney
You may have seen or searched for “what does BAC stand for,” “BAC meaning driving,” or “what is the legal BAC in California” when researching Driving Under the Influence, drunk driving, blood alcohol level, and chemical test results. Below are clear answers to those questions.
BAC stands for Blood-Alcohol Concentration.
BAC measures the percentage of alcohol in your bloodstream.
The alcohol concentration in your blood can be shown in different ways. The most common way is weight per volume, or grams/volume of blood. In California, this is shown as grams/100 milliliters of blood, gram % or percent (W/V), and grams per 210 liters of breath or g/210 L breath.1
BAC Meaning in Driving & DUI Cases
When discussing the BAC meaning in driving, California law recognizes two primary DUI theories:
Per Se DUI – 0.08% or Higher
Under California Vehicle Code 23152(b), it is unlawful to drive with a BAC of 0.08 percent or more.4 This is known as a “per se” violation, meaning the BAC level alone can establish the offense.
Impairment DUI – Below 0.08%
You can still be charged with DUI even if your BAC is below 0.08% if prosecutors claim alcohol impaired your ability to drive safely under Vehicle Code 23152(a). This is why BAC evidence must be carefully reviewed in every DUI case.
The Three-Hour Presumption
The movement of alcohol in the body — absorption, distribution, metabolism, and elimination — are dynamic processes. However, in California, there is a rebuttable presumption that says the person had 0.08 percent (or more) in his or her blood at the time of driving if the person had 0.08 percent in his or her blood at the time of the chemical test within three hours after the driving.2
Although there is little science to justify this presumption, it still applies in court and at the DMV. However, the key is that this presumption is rebuttable. That is where your DUI Lawyer plays a critical role.
It is just as likely that your BAC may be rising, falling, or staying the same over the same time period.
DUI Attorneys often consult with forensic toxicologists, who are experts on BAC. These discussions cover estimates about what a drinker’s possible BAC might be when the person was driving and/or taking the chemical tests (breath or blood tests).
There are formulas used for these estimates, and there are also factors and assumptions that can have an effect on the calculations.
It is sometimes useful to estimate how many drinks someone would have to drink to be at a certain BAC. Wine is generally 12% alcohol, while beer is about 4%. You can say that 4 ounces of wine (glass of wine) has the equivalent alcohol content to a 12-ounce beer. Furthermore, 1.25 ounces of 80-proof liquor (40% alcohol) is equal to 1 ounce of 100-proof liquor (50% alcohol).
Many experts warn of the dangers associated with what is called “extrapolating” to past BAC levels. If all that is known is the time you were pulled over by the police and the chemical test result, Dr. Kurt Dubowski, the University of Oklahoma Distinguished Professor of Medicine and Director of Toxicology Laboratories at the University of Oklahoma, says that “no forensically valid forward or backward extrapolation… is ordinarily possible.” 3
What is the legal “BAC limit” for drivers in California?
BAC Laws in California
What is the legal BAC in California?
- It is illegal to drive with a BAC of 0.08 percent or more if you are 21 or older.4
- It is illegal for someone under 21 to drive with a BAC of 0.05 percent or more.5
- It is also unlawful for a person under 21 to drive with a BAC of 0.01 percent or more under California’s Zero Tolerance law.6
- It is illegal to drive with a blood-alcohol concentration of 0.08 percent or higher and cause injury to someone else.7
- It is unlawful for commercial drivers and “passenger for hire” drivers to drive with a BAC of 0.04 percent or more.8
High BAC Enhancement
A BAC of 0.15 percent 9 and 0.20 percent 10 will cause the prosecutor to file sentence enhancements for high BAC. This is how the prosecutor signals to the judge to increase your penalties under California law.
If you face this situation, it is highly recommended that you call California DUI Attorney Richard Wagner at (714) 721-4423.
Potential challenges to BAC evidence:
Attacks on Breath Tests
If you took a breath test while in the absorptive phase, your breath alcohol concentration (BrAC) would be higher than your BAC. 11
There can also be alcohol contamination in your mouth from recent drinking, regurgitation, burping, or vomiting. If the officer failed to properly administer the breath test to you, the BAC results are unreliable.
The breath sample shall be collected only after fifteen continuous minutes, during which time the subject must not have ingested alcoholic beverages or other fluids, regurgitated, vomited, eaten, or smoked. 12
A DUI Defense attorney should also review the calibration records of the breath machine to see if it was properly maintained.
Read more about Understanding DUI Breath Testing in California
Attacks on Blood Tests
If you took a blood test, DUI Defense Attorneys attack the collection, transportation, and storage of your blood sample.
- Was the person who took your blood qualified to draw your blood?
- Was your blood taken in a reasonable manner according to acceptable medical practices?
- Was your sample properly preserved?
Alcohol in the blood vial can be produced by contamination. Alcohol can be produced by fermentation. 13 The device analyzing your blood cannot tell where the alcohol came from. Therefore, the lab report may not reflect your actual BAC.
Read more: Understanding DUI Blood Tests in California
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Frequently Asked Questions About BAC
What does BAC stand for?
BAC stands for Blood Alcohol Concentration. It measures the percentage of alcohol in a person’s bloodstream.
What is the legal BAC in California?
For most adult drivers, the legal BAC limit is 0.08%. Lower limits apply to commercial drivers and drivers under 21.
Can you get a DUI below 0.08%?
Yes. California law allows DUI charges if you are impaired, even if your BAC is below 0.08%.
What is considered a high BAC in California?
A BAC of 0.15% or higher is often treated as a high BAC case and may lead to enhanced penalties.
LEGAL AUTHORITIES
1 California Vehicle Code Section 23152(b), “For purposes of this article …, percent, by weight, of alcohol in a person’s blood is based upon grams of alcohol per 100 milliliters of blood or grams of alcohol per 210 liters of breath.”
2 California Vehicle Code Sections 23152(b) and 23153(b), “In any prosecution under this subdivision, it is a rebuttable presumption that the person had 0.08 percent or more, by weight, of alcohol in his or her blood at the time of driving the vehicle if the person had 0.08 percent or more, by weight, of alcohol in his or her blood at the time of the performance of a chemical test within three hours after the driving.”
3 Kurt M. Dubowski, Ph.D., “Absorption, Distribution and Elimination of Alcohol: Highway Safety Aspects,” Journal of Studies on Alcohol, (July 1985), p. 106.
4 California Vehicle Code Section 23152(b), “It is unlawful for a person who has 0.08 percent or more, by weight, of alcohol in his or her blood to drive a vehicle.”
5 California Vehicle Code Section 23140(a), “It is unlawful for a person under the age of 21 years who has 0.05 percent or more, by weight, of alcohol in his or her blood to drive a vehicle.”
6 California Vehicle Code Section 23136(a), “Notwithstanding Sections 23152 and 23153, it is unlawful for a person under the age of 21 years who has a blood-alcohol concentration of 0.01 percent or greater, as measured by a preliminary alcohol screening test or other chemical test, to drive a vehicle.”
7 California Vehicle Code Section 23153(b), “It is unlawful for a person, while having 0.08 percent or more, by weight, of alcohol in his or her blood to drive a vehicle and concurrently do any act forbidden by law, or neglect any duty imposed by law in driving the vehicle, which act or neglect proximately causes bodily injury to any person other than the driver.”
8 California Vehicle Code Section 23152(d), “It is unlawful for a person who has 0.04 percent or more, by weight, of alcohol in his or her blood to drive a commercial motor vehicle, as defined in Section 15210. In a prosecution under this subdivision, it is a rebuttable presumption that the person had 0.04 percent or more, by weight, of alcohol in his or her blood at the time of driving the vehicle if the person had 0.04 percent or more, by weight, of alcohol in his or her blood at the time of the performance of a chemical test within three hours after the driving.”
California Vehicle Code Section 23152(e), “Commencing July 1, 2018, it shall be unlawful for a person who has 0.04 percent or more, by weight, of alcohol in his or her blood to drive a motor vehicle when a passenger for hire is a passenger in the vehicle at the time of the offense. For purposes of this subdivision, “passenger for hire” means a passenger for whom consideration is contributed or expected as a condition of carriage in the vehicle, whether directly or indirectly flowing to the owner, operator, agent, or any other person having an interest in the vehicle. In a prosecution under this subdivision, it is a rebuttable presumption that the person had 0.04 percent or more, by weight, of alcohol in his or her blood at the time of driving the vehicle if the person had 0.04 percent or more, by weight, of alcohol in his or her blood at the time of the performance of a chemical test within three hours after the driving.”
9 California Vehicle Code 23578, “In addition to any other provision of this code, if a person is convicted of a violation of Section 23152 or 23153, the court shall consider a concentration of alcohol in the person’s blood of 0.15 percent or more, by weight, … as a special factor that may justify enhancing the penalties in sentencing, in determining whether to grant probation, and, if probation is granted, in determining additional or enhanced terms and conditions of probation.”
10 California Vehicle Code Section 23538(b)(2), “The court shall refer a first offender whose blood-alcohol concentration was 0.20 percent or more, by weight, … to participate for at least nine months or longer, as ordered by the court, in a licensed program that consists of at least 60 hours of program activities, including those education, group counseling, and individual interview sessions …”
11 Gerald D. Simpson, “Accuracy and Precision of Breath Alcohol Measurements for a Random Subject in Postabsorptive State,” Clinical Chemistry 33/2, 261-268 (1987).
12 17 CCR 1221.1(b)(1), “The breath sample shall be collected only after fifteen continuous minutes during which time the subject must not have ingested alcoholic beverages or other fluids, regurgitated, vomited, eaten, or smoked.”
13 Blume, P. and Lakatua, D.J., “The effect of microbial contamination of the blood sample on the determination of ethanol levels in serum,” Am. J. Clin. Path. 60:700-702 (1973); Chang, R.B. et al, “The stability of ethyl alcohol in forensic blood specimens,” J. Anal. Toxicol. 8:66-67 (1984).
