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

In every U.S. state, the legal blood alcohol content (BAC) limit for driving is 0.08%. This means 0.08 grams of alcohol per 100 milliliters of blood. If a breath or blood test shows you at or above this level, you can be arrested for driving under the influence, even if you feel fine and drive without incident.

The 0.08% standard has been federal law since 2000, when the government tied highway funding to states adopting this limit. Before that, some states allowed 0.10%. The limit applies to anyone 21 or older operating a motor vehicle on a public road. Different, lower limits explore to drivers under 21 and to commercial drivers, which are covered separately below.

What matters for your situation: you can be charged with DUI at 0.08% or higher. You can also be charged below 0.08% if an officer believes your driving was impaired by alcohol or drugs — the BAC number is not a shield, only a threshold where the law presumes impairment.

Key Takeaways

  • The legal limit of 0.08% BAC applies to all drivers 21 and older in every state, and exceeding it is grounds for arrest.
  • Drivers under 21 face arrest at 0.02% BAC or any detectable alcohol; commercial drivers face arrest at 0.04% BAC.
  • You can be arrested for DUI below 0.08% if an officer observes impaired driving, because the limit is not a legal threshold for drinking and driving.
  • BAC rises differently depending on body weight, food intake, drinking speed, and metabolism, so the same number of drinks produces different results for different people.
  • Breath tests and blood tests measure BAC differently and have different margins of error; you have the right to request a blood test if stopped.

How BAC is measured and what the numbers mean

Police measure BAC through a breath test (breathalyzer) or a blood test. A breath test estimates BAC by measuring alcohol in your lungs; a blood test directly measures alcohol in your bloodstream. Breath tests are faster and happen roadside, but blood tests are more precise and are used to confirm a breath result or when breath testing is not possible.

The 0.08% figure is a concentration: 0.08 grams of alcohol per 100 milliliters of blood. To understand what this means in drinks, you need to know that BAC depends on much more than how many drinks you consumed. A person's weight, sex, food intake, drinking speed, and metabolism all affect how quickly alcohol enters the bloodstream and how long it stays there. The same three drinks will produce a BAC of roughly 0.06% in a 200-pound person but roughly 0.09% in a 140-pound person, assuming similar conditions.

Standard drink sizes matter too. One standard drink in the U.S. is 12 ounces of beer (5% alcohol), 5 ounces of wine (12% alcohol), or 1.5 ounces of liquor (40% alcohol). A mixed drink at a bar often contains more than 1.5 ounces of liquor, so you may be consuming more than one standard drink without realizing it.

Lower limits for drivers under 21 and commercial drivers

Drivers under 21 face a zero-tolerance standard in all states: any detectable alcohol is grounds for arrest, though the legal threshold is usually set at 0.02% BAC to account for trace amounts from food or mouthwash. This is much stricter than the 0.08% limit for adults.

Commercial drivers — those operating a truck, bus, or other vehicle requiring a commercial driver's license — face arrest at 0.04% BAC, half the standard limit. This applies whether the driver is operating a commercial vehicle at the time or driving a personal vehicle off-duty. Some states also impose additional penalties on commercial drivers, such as longer license suspensions.

What happens if you are stopped and tested

If a police officer believes you are impaired, they will ask you to perform field sobriety tests (walking in a straight line, standing on one leg, following a moving object with your eyes). These are voluntary, though refusing may be used against you. The officer will then ask you to take a breath test, usually at the roadside or at the police station.

You have the right to refuse a breath test, but refusal has consequences. In most states, refusing a breath or blood test results in an automatic license suspension, often longer than the suspension for a DUI conviction itself. Some states treat refusal as evidence of guilt in court. If you refuse, you can usually request a blood test instead, which is more accurate but takes longer.

If the test shows 0.08% or higher, you will be arrested and taken to the police station for booking. You will be given the opportunity to call a lawyer. Do not answer questions about drinking or driving without a lawyer present — anything you say can be used against you in court.

How BAC changes over time and why timing matters

BAC does not rise when ready when you drink. Alcohol enters the bloodstream through the stomach and small intestine, a process that takes 15 to 45 minutes depending on whether you have eaten. Your BAC peaks when absorption is complete, then declines as your liver metabolizes the alcohol. The liver processes roughly one standard drink per hour, though this varies by person.

This timing matters because you can be over the legal limit hours after your last drink. If you drank heavily at dinner and drove home at midnight, your BAC might still be rising or at its peak. If you drank at a bar and drove home an hour later, your BAC might be higher than when you left the bar. Conversely, if you are tested several hours after drinking, your BAC will be lower than it was at the time you were driving, which is why the prosecution must prove what your BAC was at the time of driving, not at the time of testing.

Breath test accuracy and your right to a blood test

Breath tests estimate BAC and have a margin of error. The machine assumes a fixed ratio between alcohol in your breath and alcohol in your blood, but this ratio varies between individuals. Breath tests can be affected by mouth alcohol (from mouthwash, breath spray, or vomit), by certain medical conditions, and by improper calibration of the machine.

Blood tests directly measure alcohol in your blood and are more accurate than breath tests. If you are arrested and given a breath test, you have the right to request a blood test as well. Some states allow you to request a blood test instead of a breath test. If you request a blood test, the officer must honor the request, though they may proceed with a breath test first and then obtain a blood sample later.

The blood sample is split: one portion is tested by the police, and you have the right to have the other portion tested by an independent laboratory of your choice. This is important because it gives you evidence if the police lab result is wrong.

State variations and enhanced penalties

While the 0.08% limit is uniform across all states, penalties for exceeding it vary. Some states impose harsher penalties for higher BAC levels — for example, a BAC of 0.15% or higher may result in longer license suspension, higher fines, or mandatory jail time compared to a BAC between 0.08% and 0.14%. A few states have an "aggravated DUI" category for BAC above a certain threshold, usually 0.15% or 0.20%.

License suspension length also varies by state and by whether it is a first offense. A first DUI conviction typically results in a suspension of three months to one year. Refusal to take a test often triggers an automatic administrative suspension separate from any criminal penalty.

Frequently Asked Questions

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

Yes. The 0.08% limit is a threshold where the law presumes impairment, but you can be arrested below that level if an officer observes signs of impairment: swerving, slow reaction time, slurred speech, or poor performance on field sobriety tests. The prosecution must prove impairment, but they do not need a BAC reading to do so.

How long does alcohol stay in your system?

Your liver metabolizes roughly one standard drink per hour. A person with a BAC of 0.08% will reach 0.00% in approximately eight hours, assuming no additional drinking. However, BAC continues to rise for 15 to 45 minutes after your last drink, so you may still be over the limit hours after you stopped drinking.

Does food affect how quickly you get drunk?

Yes. Eating before or while drinking slows alcohol absorption, which delays the rise in BAC and lowers your peak BAC. Drinking on an empty stomach causes alcohol to enter the bloodstream faster, raising your BAC more quickly and to a higher level for the same number of drinks.

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 across states. Some states use DUI for alcohol and DWI for drugs; others use them interchangeably. Check your state's laws to understand which term applies to your situation.

Can I refuse a breath test without consequences?

You can refuse, but refusal triggers an automatic license suspension in most states, often longer than the suspension for a DUI conviction. Refusal may also be used as evidence against you in court. You can usually request a blood test instead, which is more accurate but takes longer to obtain.