What is the legal “BAC limit” for drivers in California?

Driving in California with a blood alcohol concentration (BAC) of 0.08% or higher is an automatic DUI. Though if you are under 21, you can get a DUI by driving with a BAC of only 0.05%.

Meanwhile, the legal limit is even lower if you are a rideshare driver or have a CDL: You can get a DUI by driving with a BAC of just 0.04%.

Even if your blood alcohol content is legal, you can still be convicted of DUI in California if alcohol or drugs are impairing your ability to drive safely.

To help you better understand the law, our California DUI defense lawyers explain 8 critical points about BAC:

• 1. What is BAC?
• 2. When To Stop Drinking
• 3. Breath and Blood Tests
• 4. DUI BAC Limits
• 5. DUI Investigation and Arrest
• 6. DUI Prosecutions
• 7. Breath v. Blood
• 8. Defenses
• Additional Resources

1. What is BAC?

Blood alcohol concentration (“BAC”) is a measure of the amount of alcohol in your bloodstream. It is also referred to as:

• “blood alcohol content” or
• “blood alcohol level.”¹

Blood alcohol content is expressed as a percentage – for instance 0.08% (the California DUI limit for most adult drivers).² This percentage represents the grams of alcohol present in every 100 milliliters of your blood.³

A higher number indicates that you have more alcohol in your system. A lower number indicates less alcohol.

2. When To Stop Drinking

If you are like most people, your BAC will hit 0.08% – making it illegal to drive – after only two or three:

• 12-ounce beers,
• five-ounce wine glasses, or
• shots.⁴

However, everyone is different and metabolizes alcohol at their own rate.

Note that if your blood alcohol content reaches .40%, you may suffer alcohol poisoning, unconsciousness, and potentially death. You should stop drinking if you experience:

• nausea or vomiting,
• a body temperature lower than 98.6 degrees,
• blue-ish skin,
• confusion,
• fatigue, and/or
• irregular breathing.⁵

Ideally, you should not drink anything if you are going to drive. For some people, only one drink is enough to impair your driving.

3. Breath and Blood Tests

BAC is measured by either a DUI breath test or a DUI blood test. Both are considered reliable when properly administered. Both are admissible in court.

Let’s take a closer look at each of them.

DUI Breath Tests

The most commonly used test for BAC is a breath test. They are minimally invasive and deliver instant results.

Breath tests in California fall into two basic categories (discussed further below):

• Pre-arrest “preliminary alcohol screening” (“PAS) tests, and
• Post-arrest evidentiary breath tests.

How DUI Breath Tests Measure Blood Alcohol

A breath test does not directly measure the percentage of alcohol in your blood. Instead, it measures the alcohol present in the deepest part of your lungs, where it is closest to your blood supply.

A “Breathalyzer”-style machine then mathematically converts this amount into an approximately equivalent blood alcohol percentage. The formula it uses to do this is known as a “partition ratio.”

In actual fact, partition ratios can differ from person to person and situation to situation. However in California, by law, the partition ratio is deemed to be 2,100 to 1.⁶ This means that the amount of alcohol present in 2,100 milliliters of deep lung breath is considered legally equal to the amount of alcohol in 1 milliliter of blood.

Preliminary Alcohol Screening (PAS) Tests

A preliminary alcohol screen (PAS) test is given before you are arrested for DUI. Typically, this occurs after a traffic stop or at a DUI sobriety checkpoint.

You may decline a pre-arrest PAS test unless:

• You are under 21 years of age,⁷ or
• You are on probation for a prior DUI offense.⁸

Post-Arrest DUI Breath Tests

After you have been lawfully arrested for DUI, you will be given the choice of a

• breath test or
• blood test.

You must take this test even if you previously took a PAS breath test.⁹ Consequences of refusing to take a chemical test include the automatic suspension of your driver’s license for at least one year.¹⁰

Most people elect to take the breath test as it is less invasive. This post-arrest breath test is usually given on a desktop device at the police station. Otherwise, it is similar to a PAS test.

In some counties, the police may give this post-arrest breath test roadside. In this case, it will appear similar to a PAS test. The important difference, however, is that unlike a PAS test, a post-arrest test is not optional, no matter where it is given.

DUI Blood Tests

Blood tests directly measure the alcohol in your blood. This makes them the most accurate test for determining your blood alcohol concentration—at least when everything is done strictly according to the procedure.

Your blood will be taken by someone licensed by the state.¹¹ Part of this sample will be sent to a lab for analysis. It can take several weeks for us to get these test results.

The main advantage of a DUI blood test over a DUI breath test is that part of the sample can be saved. This means we can get a hold of it and have it independently tested.¹²

As Riverside DUI defense attorney Michael Scaffidi¹³ explains,

“When a client chooses a blood test, we can file a California DUI ‘blood split’ motion. This lets us obtain part of the same blood sample the police used and have it sent to a lab of our choice for independent testing. If the results are different, we can often use them to challenge the prosecution’s case.”

Can BAC be measured by a urine test?

Blood alcohol concentration is not normally measured by a urine test in California DUI cases. Urine tests can accurately detect the presence of alcohol, but they are less reliable than blood tests or breath tests for determining the specific amount of alcohol present.

So a urine test will only be used in a California drunk driving case if:

• Both a blood and breath test are unavailable, or
• You are incapable of taking one of the tests, and the other one is unavailable.¹⁴

Reasons you might be incapable of taking a blood or breath test can include:

• A medical condition (such as a breathing or clotting disorder), or
• An extremely high level of inebriation (making it difficult to complete a breath test).

4. DUI BAC Limits

By law, driving with more than a certain amount of alcohol in your system is considered driving under the influence. This is known as a “per se” DUI.¹⁵  In such a case, the prosecutor does not need to prove that your driving was actually impaired.

California’s DUI “per se” code sections are:

• Vehicle Code 21352(b) – driving with a BAC of .08% or higher (adults, non-commercial vehicles),
• Vehicle Code 23140 – underage DUI with a BAC of .05% or higher (drivers under 21),
• Vehicle Code 23152(d) – commercial DUI with a BAC of .04% or higher (drivers of commercial vehicles), and
• Vehicle Code 23152(e) – “passenger for hire” DUI with a BAC of .04% or higher (taxi, limo, Uber and Lyft drivers, etc.).

It is also against the law to drive with any blood alcohol content (0.01% or higher) if you are either:

• under 21 years old (Vehicle Code 23136); or
• on DUI probation (Vehicle Code 23154).

Violating these “zero tolerance” laws is not technically DUI, though you face a license suspension.

The following chart outlines the penalties for driving with an illegal BAC:

Offense	Illegal BAC	California Penalties (1st offense)
“Zero tolerance” — VC 23136	.01%	1-year driver’s license suspension
Commercial DUI — VC 23152(d)	.04%	1-year driver’s license suspension; 3-5 years misdemeanor probation; $390-$1,000 fine; alcohol education program; up to 1 year in county jail
Rideshare DUI — VC 23152(e)	.04%	6-10-month driver’s license suspension; 3-5 years misdemeanor probation; $390-$1,000 fine; alcohol education program; up to 6 months in county jail
Underage DUI — VC 23140	.05%	1-year driver’s license suspension; $100 fine; alcohol education program
Standard (“adult”) DUI — VC 23152(b)	.08%	6-10-month driver’s license suspension; 3-5 years misdemeanor probation; $390-$1,000 fine; alcohol education program; up to 6 months in county jail

5. DUI Investigation and Arrest

Police measure your BAC at two stages of the California DUI court process:

1. The investigation, and
2. The arrest.

The DUI Investigation

During a traffic stop, if the officer suspects you of being under the influence, they may start a DUI investigation. As part of the investigation, the officer may ask you to take a PAS test.¹⁶

If you “blow” a BAC below the legal limit, the officer will usually let you go with just a traffic ticket or a warning.

If the test is positive, the officer will probably arrest you and require a post-arrest breath or blood test.

Should I agree to a PAS test?

If you are an adult driver who thinks you may be over the legal limit, you are usually not well-served by taking a PAS test. You can (and probably should) politely decline to take one. The officer may arrest you anyway.

If you think you are under the legal limit, you also have the right to decline. You may prefer, however, to take the test in order to show the officer that you are not drunk.

Note that if you are under the age of 21 or on DUI probation, you may not refuse a PAS without consequences.¹⁷

The DUI Arrest

A post-arrest chemical test is considered “evidentiary.” This means a prosecutor can use it in court as evidence that you drove drunk.

You cannot refuse this type of chemical test without consequences.¹⁸

You must usually be offered the choice of a breath or blood test.¹⁹ Though in some cases, the officer can require testing of your blood. This can be done instead of (or in addition to) a breath reading if the officer reasonably believes you are under the influence of drugs.²⁰

6. DUI prosecutions

During a California DUI case, the prosecutor will use BAC and other evidence to prove that you either:

• were over the legal limit and, therefore, guilty of a DUI per se in violation of VC 23152(b), and/or
• were actually impaired and, therefore, guilty of driving under the influence in violation of VC 23152(a).

DUI per se relies on an “objective” measurement of impairment. If your BAC is at or above a specified level (such as 0.08% for an adult in a non-commercial vehicle), you are legally considered too drunk to drive.

Driving under the influence is a “subjective” test. The prosecutor must show that you were unable to drive safely due to alcohol. Evidence in addition to your blood alcohol level is usually required, such as:

• Testimony from the arresting officer about your driving pattern and physical symptoms of intoxication,
• Proof of when you drove, and
• Testimony from other witnesses (including passengers in your vehicle, if any).

7. Breath v. Blood

Unfortunately, there is no easy answer as to the best chemical test to pick after a DUI arrest. Each has its advantages, as discussed below.

Advantages of a Breath Test

Most people arrested for DUI choose to take a breath test. The main advantages of a breath BAC measurement are that:

1. It is less invasive and less stressful for most people, and
2. The results are available right away.

Advantages of a Blood Test

The main advantages of a DUI blood test are that:

1. A blood sample allows a more accurate assessment of BAC than a breath sample. This can be useful when you are very close to the legal limit.
2. Part of the blood sample can be saved and independently tested by a lab of your choosing. Breath samples are not preserved.

Advantages of Refusing the Test

The one advantage of refusing a chemical test is that there will be no way to prove your BAC. The prosecution will have to prove guilt by showing that your driving was actually impaired by alcohol and/or drugs.

However, a refusal to take a chemical test is itself admissible as evidence of guilt.²¹ (Note that this does not apply to a PAS test unless you are under 21 or on DUI probation).²²

Plus you face consequences for the test refusal, including:

• Automatic suspension of your driver’s license for at least one year,
• Additional time in jail if you are convicted of driving under the influence, and
• Nine months of DUI school (instead of the usual three months) if you are convicted.²³

Despite the consequences of a refusal, it might be a good choice if:

• You do not depend on driving to get around (and can, therefore, afford to suffer the automatic driver’s license suspension), and/or
• You are very drunk and do not want to suffer the additional consequences of driving with a very high BAC (0.15% or higher).²⁴

8. Defenses

Just because a breath or blood test showed a certain BAC, it does not mean the results were accurate. We discuss potential inaccuracies at length in our articles on:

• DUI blood testing errors, and
• DUI breath testing errors.

In general, we can challenge blood alcohol level results by arguing:

• The officer did not properly advise you of the choices and consequences involved in taking DUI chemical tests;
• The officer did not observe proper procedures during the administration of the DUI test;
• The testing equipment was not calibrated as required under California law;
• The breath or blood sample was mishandled and possibly contaminated;
• You suffered from a medical condition such as GERD or diabetes that resulted in a falsely elevated BAC reading;
• You were on a high-protein/low-carb diet;
• There was “residual mouth alcohol” in your mouth;
• You had “rising blood alcohol” at the time of the test (meaning your BAC was lower at the time of driving).

Also see our related article, “20 Legal Defenses for Fighting California DUI Charges.”

Additional Resources

For more information, refer to the following:

• California Driver’s Handbook: Alcohol and Drugs – Legal information provided by the California Department of Motor Vehicles.
• BAC Legal Limits in Different States, Counties, & Cities – General information by American Addiction Centers.
• The effectiveness of reducing illegal blood alcohol concentration (BAC) limits for driving: Evidence for lowering the limit to .05 BAC – Scholarly article in Journal of Safety Research.
• Moving beyond BAC in DUI: Identifying Who Is at Risk of Recidivating – Scholarly article in Criminology & Public Policy.

---

Legal references: