The legal limit is 0.08% blood alcohol content in all 50 states
In every U.S. state, you cannot legally drive with a blood alcohol content (BAC) of 0.08% or higher. This is the threshold where the law treats you as impaired, regardless of how you feel or how well you think you're driving. A standard drink—12 ounces of beer, 5 ounces of wine, or 1.5 ounces of spirits—raises your BAC by roughly 0.02%, though this varies based on your weight, sex, food intake, and metabolism.
The 0.08% limit has been federal law since 2000, when states adopted it to receive highway funding. Before that, some states allowed 0.10%. The limit applies to drivers 21 and older. Drivers under 21 face a zero-tolerance rule in most states: any detectable alcohol can result in a DUI charge. Commercial drivers have a lower limit of 0.04%.
Key Takeaways
- The legal BAC limit for drivers 21 and older is 0.08% in all states; drivers under 21 and commercial drivers face stricter limits.
- You can be arrested for DUI below 0.08% if an officer observes impaired driving signs, because the law recognizes impairment happens before you reach that threshold.
- BAC rises differently depending on your weight, sex, food intake, and how fast you drink, so there is no safe number of drinks you can count on.
- A breath test at the roadside is not admissible in court; only a breath or blood test at the station or hospital can be used as evidence.
- Refusing a breath or blood test carries the same penalties as a DUI conviction in most states, including license suspension.
Why impairment starts before 0.08%
The 0.08% limit is a legal threshold, not a safety threshold. Impairment begins at lower BAC levels. At 0.02%, you lose the ability to track moving objects and your steering becomes less precise. At 0.05%, you have reduced coordination and difficulty steering. At 0.08%, you have poor muscle control and impaired judgment, but the damage to your driving has already happened.
This is why you can be arrested for DUI even if your BAC is below 0.08%. If an officer observes you weaving, failing field sobriety tests, or showing other signs of impairment, they can charge you with DUI under what's called "impaired to any degree" laws. Many states use this language specifically to catch drivers who are genuinely unsafe but haven't reached the 0.08% mark yet.
How BAC is measured and what the numbers mean
Police measure BAC through a breath test (breathalyzer) or a blood test. The breath test estimates BAC by measuring alcohol in your lungs; the blood test measures it directly in your blood. Breath tests are faster and happen at the roadside or station. Blood tests are more accurate but require a needle and take longer.
The percentage refers to grams of alcohol per 100 milliliters of blood. A BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood. The following table shows how BAC typically progresses with standard drinks, though individual variation is significant:
| Standard Drinks | Approximate BAC (150 lb person) | Typical Effects |
|---|---|---|
| 1 | 0.02% | Slight warmth, relaxation |
| 2 | 0.04% | Mild impairment, reduced alertness |
| 3 | 0.06% | Reduced coordination, impaired judgment |
| 4 | 0.08% | Legal impairment threshold |
| 5 | 0.10% | Slurred speech, poor muscle control |
These numbers assume one drink per hour on a full stomach. Drinking faster, on an empty stomach, or being a smaller person will raise your BAC more quickly. Women typically reach higher BAC levels than men after the same number of drinks because they have less body water to dilute the alcohol.
What happens if you refuse a breath or blood test
When an officer asks you to take a breath or blood test after arrest, you have the legal right to refuse. However, refusing carries serious consequences in most states. Your license will be suspended automatically—often for one year on a first refusal, longer on subsequent ones. This suspension happens through the Department of Motor Vehicles, separate from any DUI case.
In many states, your refusal can be used as evidence against you in court, and prosecutors can argue that you refused because you knew your BAC was high. Some states have implied consent laws, meaning that by holding a driver's license, you've already agreed to submit to testing. Violating that agreement triggers the suspension.
A few states allow you to request an independent blood test after the official one, but you must ask when ready. If you refuse the official test, you generally cannot later demand an independent test to prove your innocence.
Lower limits for specific drivers
Drivers under 21 face zero-tolerance laws in most states. Any BAC above 0.00% can result in a DUI charge, license suspension, and other penalties. Some states set the limit at 0.02% to account for trace amounts from mouthwash or food, but the intent is clear: underage drivers should not drink and drive at all.
Commercial drivers (those holding a CDL) have a 0.04% limit, half the standard limit. This applies whether they're driving a commercial vehicle or a personal car. A DUI conviction can cost a commercial driver their job and their ability to work in the industry.
Drivers on probation or with prior DUI convictions may face an even lower limit, sometimes 0.02% or 0.00%, depending on the state and the terms of their sentence. Check your probation paperwork or ask your attorney if you're unsure.
The difference between a roadside test and a legal test
A breath test at the roadside—the handheld device an officer uses during a traffic stop—is not admissible as evidence in court. It's a screening tool only. The officer uses it to decide whether to arrest you and take you to the station for an official breath test or blood draw.
The official test happens at a police station, hospital, or certified testing facility using a larger, calibrated machine. This test result is admissible in court and is what prosecutors use to prove your BAC. If you're arrested, you have the right to request an independent blood test at a hospital or lab of your choice, though you usually have to pay for it yourself.
Field sobriety tests—walking a line, standing on one leg, following a pen with your eyes—are also not chemical tests. They're observations of your coordination and balance. An officer can use them to justify an arrest, but they're subjective and can be affected by fatigue, medical conditions, or even the surface you're standing on.
State variations in DUI penalties
While the 0.08% limit is uniform, the penalties for exceeding it vary by state. A first DUI conviction typically results in a license suspension (usually 3 to 12 months), fines ($500 to $2,000), and possible jail time (up to 6 months). Some states require an ignition interlock device, which prevents your car from starting if it detects alcohol on your breath.
Repeat offenses carry harsher penalties. A second DUI within 10 years may mean a longer suspension, higher fines, and mandatory jail time. A third or fourth offense can result in felony charges, years in prison, and permanent license revocation in some states.
If you caused an accident or injury while impaired, you face additional charges like reckless driving or assault. If someone died, you could be charged with vehicular manslaughter or DUI homicide, which carry prison sentences of years or decades.
Frequently Asked Questions
Can I be arrested for DUI if my BAC is below 0.08%?
Yes. Many states have impaired-to-any-degree laws that allow arrest if an officer observes signs of impairment—weaving, failing field sobriety tests, slurred speech—regardless of your BAC. Impairment begins at lower levels than 0.08%, so the legal threshold is not the same as the safety threshold.
How long does alcohol stay in your system?
Your body metabolizes roughly one standard drink per hour. A breath test can detect alcohol for 12 to 24 hours after drinking, and a blood test for 24 to 48 hours. However, BAC drops as time passes, so a test hours after you stopped drinking will show a lower level than one taken when ready.
Does eating food before drinking lower my BAC?
Food slows alcohol absorption, so your BAC rises more slowly if you eat before or while drinking. However, it does not prevent alcohol from reaching your bloodstream or lower your peak BAC—it just delays it. You will eventually reach the same BAC level; it just takes longer.
What if I blow into a breathalyzer and it shows 0.08% but I feel fine?
How you feel is irrelevant to the law. You are legally impaired at 0.08% regardless of whether you feel drunk. Many people underestimate their impairment because alcohol affects judgment and self-awareness. If a test shows 0.08% or higher, you are over the legal limit.
Can I fight a DUI charge if the breath test was inaccurate?
Yes. Breath tests can be challenged if the machine was not properly calibrated, the officer did not follow testing procedures, or you had a medical condition affecting the result. You can request an independent blood test and hire an attorney to examine the testing records and procedures used.