The legal limit for drunk driving is a blood alcohol concentration (BAC) of 0.08% in all 50 states, the District of Columbia, and most U.S. territories for drivers age 21 and older

This means that if a breath or blood test shows your BAC at or above 0.08%, you can be arrested and charged with driving under the influence (DUI) or driving while intoxicated (DWI), depending on your state's terminology. The 0.08% standard has been federal law since 2000, though the specific name of the offense and the exact penalties vary by state.

The limit exists because at 0.08% BAC, most people show measurable impairment in reaction time, judgment, and motor control — the abilities most critical to safe driving. You do not have to feel drunk, appear drunk, or admit to drinking to be charged. A test result is evidence on its own.

Key Takeaways

  • The legal BAC limit for drivers 21 and older is 0.08% in every state, measured by breath or blood test.
  • Drivers under 21 face a lower limit of 0.02% BAC in most states, and commercial drivers have a limit of 0.04%.
  • You can be arrested for DUI even if your BAC is below 0.08% if an officer observes signs of impairment or you refuse a test.
  • Penalties for exceeding the limit include license suspension, fines, jail time, and mandatory programs, with severity increasing for repeat offenses.
  • The BAC limit applies only to operation of a vehicle; sitting in a parked car with the engine running can still result in charges in many states.

Lower limits for younger and commercial drivers

If you are under 21, the legal limit is 0.02% BAC in most states — roughly one standard drink. Some states set it even lower or use a zero-tolerance rule, meaning any detectable alcohol can result in a charge. The reasoning is that drivers under 21 are not legally permitted to drink at all, so the law treats any alcohol consumption while driving as a violation.

Commercial drivers — those operating a vehicle over a certain weight or carrying passengers for hire — face a 0.04% BAC limit, half the standard adult limit. This applies whether the driver is operating a commercial vehicle at the time or holds a commercial driver's license (CDL) and is driving any vehicle.

How BAC is measured and what counts as a "drink"

Police measure BAC through a breath test (breathalyzer) at the roadside or in a station, or through a blood test at a hospital or police facility. Breath tests are more common because they are faster and less invasive, but blood tests are considered more accurate and are often used to confirm a breath result or when a driver refuses a breath test.

One standard drink — the amount that raises BAC by roughly 0.02% in an average adult — is defined as 12 ounces of beer, 5 ounces of wine, or 1.5 ounces of distilled spirits. However, BAC depends on body weight, food consumption, metabolism, and the time over which drinks were consumed. Two people drinking the same amount can have different BAC levels. This is why the law uses a test result, not a count of drinks, as the measure.

Arrest and charges below 0.08% BAC

You can be arrested for DUI even if your BAC is below 0.08%. If an officer observes signs of impairment — slurred speech, poor balance, slow reaction time, or erratic driving — they can make an arrest based on those observations alone. This charge is sometimes called "impaired driving" or "DUI per se" depending on the state.

Refusing a breath or blood test also creates legal consequences in most states. Many states have "implied consent" laws, meaning that by driving on public roads, you consent to a test if stopped. Refusal can result in automatic license suspension, fines, and jail time — sometimes with penalties as severe as those for a DUI conviction itself.

Penalties for exceeding the legal limit

Penalties vary significantly by state and depend on whether it is a first offense, a repeat offense, and how far above the limit your BAC was. A first DUI offense typically results in license suspension (ranging from 3 months to 1 year), fines between $500 and $2,000, and possible jail time of up to 6 months. Many states also require completion of a DUI education program or substance abuse treatment.

A second offense within a set period (usually 5 to 10 years) carries harsher penalties: longer license suspension, higher fines, mandatory jail time (often 10 days to 1 year), and installation of an ignition interlock device on your vehicle. A third or subsequent offense may be charged as a felony in some states, resulting in years of imprisonment and permanent license revocation.

Beyond legal penalties, a DUI conviction affects insurance rates, employment (especially for jobs requiring a license), housing applications, and professional licenses. Some employers conduct background checks that reveal DUI convictions, and certain professions may suspend or revoke licenses based on a conviction.

Implied consent and what happens if you refuse a test

When you are arrested on suspicion of DUI, an officer will ask you to take a breath or blood test. In most states, you have the legal right to refuse, but refusal itself carries penalties. Your state's "implied consent" law means that by driving, you have already agreed to submit to testing if lawfully stopped.

Refusing a test typically results in automatic license suspension — often longer than the suspension for a DUI conviction — plus fines and possible jail time. Some states allow a first refusal to be treated less severely than a conviction, but a second refusal within a certain period is treated more harshly. In court, a refusal can be used as evidence against you, though it cannot be used to prove your BAC directly.

Parked vehicles and other situations where the limit applies

The 0.08% limit applies to operating a vehicle, not straightforward sitting in one. However, many states define "operating" broadly. In some places, sitting in the driver's seat with the engine running — even if the car is parked — can result in a DUI charge. A few states extend the law to include sitting in a parked car with the keys in the ignition, regardless of whether the engine is running.

The specifics depend on your state's DUI statute. If you are concerned about this situation, the safest approach is to move to the passenger seat or leave the vehicle entirely if you have been drinking and need to rest before driving.

Frequently Asked Questions

Can I be charged with DUI if I was not driving, only sitting in my car?

It depends on your state's law and the circumstances. If the engine is running or the keys are in the ignition, many states allow a DUI charge even if the car is parked. Some states require that you actually be driving. Check your state's specific statute or ask a local attorney to be certain of the rule where you live.

What is the difference between DUI and DWI?

The terms are used differently across states. DUI (driving under the influence) is the federal standard and is used in most states. DWI (driving while intoxicated) is used in some states to mean the same thing, while others use DWI for alcohol and DUI for drugs. A few states distinguish between the two based on BAC level or severity. Check your state's law for the exact definitions.

If I blow into a breathalyzer at the roadside, am I required to take a formal test at the station?

A roadside breath test (preliminary alcohol screening) is often voluntary, though refusing it may give an officer more reason to arrest you. Once arrested, an officer will ask you to take a formal breath or blood test at a station or hospital. At that point, refusal has legal consequences under your state's implied consent law. You have the right to refuse, but the refusal itself can be penalized.

Does the 0.08% limit explore to prescription medications?

The 0.08% limit applies to alcohol only. However, you can still be charged with DUI for driving under the influence of prescription medications if they impair your ability to drive safely. An officer may observe signs of impairment and make an arrest based on those observations, separate from any BAC test.

How long does alcohol stay in your system?

The body metabolizes roughly one standard drink per hour, though this varies by individual. A breath test can detect alcohol for a few hours after consumption, while a blood test can detect it for up to 12 hours. An alcohol urine test can show alcohol for up to 48 hours. The time depends on how much you drank, your body weight, and your metabolism.