The legal limit is 0.08% blood alcohol content in all 50 states for drivers 21 and older

Every state sets the same threshold: a driver with a blood alcohol content (BAC) of 0.08% or higher is considered impaired under the law. This number comes from federal highway safety standards, so it does not change by state or by the type of vehicle you drive. A breathalyzer or blood test showing 0.08% or above gives law enforcement grounds to arrest you for driving under the influence.

The 0.08% limit applies to drivers 21 and older. Drivers under 21 face a lower limit — usually 0.02% or zero tolerance, depending on the state — because they are not legally permitted to drink at all. Commercial drivers have a separate limit of 0.04%, which is half the standard limit.

One important detail: you can be charged with DUI even if your BAC is below 0.08%. If an officer observes impaired driving — swerving, failing field sobriety tests, slurred speech — they can arrest you based on those signs alone. The 0.08% number is a legal threshold, not a safe threshold or a line below which you are protected.

Key Takeaways

  • The legal limit is 0.08% BAC for drivers 21 and older in every state, set by federal highway safety standards.
  • Drivers under 21 face a lower limit (usually 0.02% or zero tolerance) because they cannot legally drink.
  • Commercial drivers have a 0.04% limit, which is half the standard limit.
  • You can be arrested for DUI below 0.08% if an officer observes signs of impairment like swerving or failing sobriety tests.
  • BAC is measured by breathalyzer or blood test, and the results are used as evidence in court.

How BAC is measured and what the numbers mean

Blood alcohol content is expressed as a percentage of alcohol in your bloodstream. A BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood. The two main ways to measure it are a breathalyzer test (which estimates BAC from your breath) and a blood test (which directly measures alcohol in a blood sample).

Breathalyzers are faster and used roadside, but blood tests are more precise and harder to challenge in court. If you refuse a breathalyzer, an officer can obtain a warrant for a blood test. The results of either test become evidence in a DUI case and can be used to prove impairment.

BAC rises and falls based on how much you drink, how fast you drink it, your body weight, food in your stomach, and your metabolism. Two people drinking the same amount can have different BAC levels. This variation is why the law sets a single threshold rather than trying to measure impairment directly — the 0.08% line is a legal standard, not a measure of how drunk you actually feel.

What happens if you are stopped and tested

If an officer suspects you of driving under the influence, they will ask you to perform a field sobriety test (walking a line, standing on one leg, following a pen with your eyes). These tests are voluntary, but refusing them can be used against you in court. After the field tests, the officer will ask you to take a breathalyzer.

In most states, you have the right to refuse a breathalyzer at the roadside. However, refusing has consequences: your driver's license can be suspended when ready, and the refusal itself can be used as evidence of guilt in court. Some states treat refusal as seriously as a failed test.

If the breathalyzer shows 0.08% or higher, you will be arrested. You will be taken to a police station or hospital for a more precise blood test. You have the right to request your own independent blood test at your own expense, and you should do so if you believe the results are wrong — this test can be used as evidence in your defense.

The difference between legal limit and impairment

The 0.08% legal limit is not the same as the point at which you become impaired. Research shows that impairment begins at much lower BAC levels — some studies suggest noticeable effects at 0.02% or 0.03%. The 0.08% threshold is a legal line drawn by lawmakers, not a scientific measure of when driving becomes unsafe.

This matters because you can be convicted of DUI without reaching 0.08%. If an officer observes impaired driving — weaving between lanes, slow reaction time, difficulty with coordination — they can arrest you and charge you with DUI. The prosecution can then use field sobriety test results, officer observations, and any BAC reading (even below 0.08%) as evidence that you were impaired.

Some states have an additional charge called "wet reckless" or impaired driving, which applies to drivers with a BAC below 0.08% but above 0.05% who show signs of impairment. The penalties are usually less severe than a full DUI conviction, but it is still a criminal charge.

How BAC limits vary for different drivers

The 0.08% limit applies to most drivers 21 and older. However, other categories of drivers face stricter limits. Drivers under 21 cannot legally drink, so most states set a zero-tolerance or near-zero limit — typically 0.02% or lower. Some states have true zero tolerance, meaning any detectable alcohol can result in a DUI charge for a minor.

Commercial drivers (those with a commercial driver's license, or CDL) have a 0.04% limit, which is half the standard limit. This applies whether they are driving a commercial vehicle or a personal vehicle. The reasoning is that commercial drivers are held to a higher safety standard because they operate large vehicles professionally.

Drivers on probation or with prior DUI convictions may face an even lower limit, sometimes 0.04% or 0.02%, as a condition of their probation or license reinstatement. You should check the terms of any probation or restricted license you have, because violating these conditions can result in additional charges.

What a DUI charge means for your record and driving privileges

A DUI conviction becomes a permanent part of your criminal record in most states. It affects employment, housing, professional licensing, and insurance rates. Even a first offense can result in jail time (usually a few days to six months), fines (typically $500 to $2,000 or more), and a suspended driver's license.

Your driver's license is usually suspended when ready after arrest, even before trial. This is called an administrative suspension and happens separately from any criminal case. You may be able to request a hearing to challenge the suspension, but you must do so within a specific time frame — usually 10 to 30 days after arrest. Missing this important date can result in an automatic suspension.

A DUI conviction also requires completion of a substance abuse program or DUI education course before your license can be reinstated. Insurance rates increase significantly after a DUI, and some insurers will not cover you at all. You may be required to carry SR-22 insurance (proof of financial responsibility) for three to five years.

Testing accuracy and your right to challenge results

Breathalyzers and blood tests are not perfect. Breathalyzers can be affected by mouth alcohol (from mouthwash or recent drinking), medical conditions like acid reflux, and calibration errors. Blood tests are more accurate but can be contaminated, mislabeled, or improperly stored. If you believe the test results are wrong, you have the right to challenge them in court.

You can request the maintenance records for the breathalyzer used in your case — if it was not properly calibrated or serviced, the results may be inadmissible. You can also request the chain of custody for a blood sample, which documents how the sample was handled from collection to testing. Any break in the chain can raise doubt about the results.

An independent blood test is your strongest defense against inaccurate results. If you request one at the time of arrest, you have the right to have it performed by a lab of your choice (though you pay for it). This test can contradict the police test and provide evidence for your defense. Some states require police to inform you of this right; others do not, so asking for it when ready is important.

Frequently Asked Questions

Can I be arrested for DUI if my BAC is below 0.08%?

Yes. If an officer observes signs of impairment — swerving, failing sobriety tests, slurred speech — you can be arrested and charged with DUI regardless of your BAC. The 0.08% threshold is a legal line, not a safe line. Some states also have separate charges for impaired driving at lower BAC levels.

What should I do if I am pulled over and asked to take a breathalyzer?

You have the right to refuse a roadside breathalyzer in most states, but refusal has consequences: your license can be suspended when ready, and the refusal can be used as evidence against you in court. If arrested, you can request an independent blood test at your own expense. Consult an attorney about your specific situation and state law.

Does food or medication affect BAC or breathalyzer results?

Food slows alcohol absorption but does not prevent it. Some medications and medical conditions (like acid reflux or diabetes) can affect breathalyzer readings. If you take medication or have a medical condition, mention it to the officer, but understand that it may not prevent arrest. This information can be used in your defense later.

What is the difference between a DUI and a DWI?

DUI stands for driving under the influence; DWI stands for driving while impaired or driving while intoxicated. The terms are used differently by different states — some use DUI for all impaired driving charges, while others distinguish between DUI (alcohol) and DWI (drugs or both). Check your state's specific definitions.

Can I get my DUI conviction removed from my record?

Some states allow expungement or record sealing of DUI convictions after a certain period (often five to ten years) and if you meet conditions like completing probation and staying out of trouble. Other states do not allow DUI expungement at all. Contact your state's court system or a local attorney to learn what is possible in your state.