Blood Alcohol Limits and DUI Laws: What Every Driver Must Know
The legal blood alcohol concentration (BAC) limit for drivers 21 and older is 0.08% in every state except Utah, where it is 0.05%. Commercial drivers are limited to 0.04%, and drivers under 21 face zero-tolerance laws, usually 0.00% to 0.02%. You can still be arrested for DUI below these limits if alcohol or drugs impair your driving.
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Alcohol and DUI quiz: 5 test-style questions
- For drivers 21 and older, the BAC limit in Utah is: 0.02% / 0.05% / 0.08% / 0.10%. Answer: 0.05%. Utah lowered its limit to 0.05% in 2018. Every other state, and the District of Columbia, uses 0.08% for drivers 21 and older.
- What is the only thing that lowers your blood alcohol concentration? Black coffee / A cold shower / Time / Eating a large meal after drinking. Answer: Time. Your liver removes alcohol at a fairly steady rate — roughly one standard drink per hour. Coffee, showers and fresh air may make you feel more alert but do not lower your BAC.
- Under implied consent laws, if you refuse a chemical test after a lawful DUI arrest: Nothing happens if you were not drunk / Your license is usually suspended automatically / You get a warning the first time / You can choose to take the test the next day. Answer: Your license is usually suspended automatically. By driving, you agree to breath, blood or urine testing when lawfully arrested for impaired driving. Refusal usually triggers an automatic administrative suspension, often longer than for failing the test.
- Which of these contains about the same amount of alcohol as a 12-ounce regular beer? A 12-ounce glass of wine / A 5-ounce glass of wine or a 1.5-ounce shot of 80-proof liquor / A pint (16 oz) of malt liquor / Two 1.5-ounce shots of liquor. Answer: A 5-ounce glass of wine or a 1.5-ounce shot of 80-proof liquor. A standard drink — 12 oz of 5% beer, 5 oz of 12% wine or 1.5 oz of 40% spirits — holds about 0.6 fluid ounces (14 grams) of pure alcohol.
- Zero-tolerance laws for drivers under 21 mean: They may drive up to 0.08% BAC / Any measurable alcohol, often 0.02% or less, can bring penalties / They are only tested after a crash / Only drivers under 18 are covered. Answer: Any measurable alcohol, often 0.02% or less, can bring penalties. Every state sets a very low limit for drivers under 21, usually 0.00% to 0.02%. Violations bring license suspension even if the driver was not visibly impaired.
Legal BAC limits in the United States
Blood alcohol concentration (BAC) measures how much alcohol is in your bloodstream. A BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood. Every state makes it illegal to drive at or above a set BAC — a “per se” limit, meaning the number alone proves the offense, whether or not you seem drunk.
| Driver | Legal limit | Notes |
|---|---|---|
| 21 and older | 0.08% | All states and D.C., except Utah |
| 21 and older in Utah | 0.05% | In effect since December 30, 2018 |
| Commercial (CDL) drivers in a commercial vehicle | 0.04% | Federal rule; any detectable alcohol takes the driver off duty for 24 hours |
| Under 21 | 0.00%–0.02% | Zero-tolerance laws in every state |
| High-BAC offenders | Often 0.15% and up | Many states impose tougher penalties above this level |
Being under the limit is not a defense if you are impaired. Officers can arrest you for DUI at any BAC if alcohol or drugs affect your driving.
How fast BAC rises: standard drinks and other factors
Permit tests often ask which drink contains the most alcohol. The trick is that a standard drink is defined by the amount of pure alcohol — about 0.6 fluid ounces or 14 grams — not by the glass. That equals 12 ounces of regular beer (about 5% alcohol), 5 ounces of wine (about 12%) or 1.5 ounces of 80-proof liquor (40%). Craft beers, large pours of wine and mixed cocktails often contain two or more standard drinks.
How high your BAC climbs depends on how much you drink and how fast, your body weight, your sex, whether you have eaten and some medications. Two people who drink the same amount can have very different BACs, and online calculators can only estimate. A smaller person can reach 0.08% after two or three drinks in an hour.
Your body removes alcohol at a roughly constant rate, often cited as about one standard drink per hour. Only time lowers BAC. Coffee, cold showers, exercise and fresh air do not, and your BAC can keep rising for a while after your last drink as alcohol is absorbed. That is also why you can still be over the limit the morning after heavy drinking.
How alcohol affects your driving
Alcohol slows the brain long before a person looks drunk. Judgment is one of the first skills affected, which is why impaired drivers often believe they are fine. NHTSA summarizes the typical effects on driving at different BAC levels:
| BAC | Predictable effects on driving |
|---|---|
| 0.02% | Decline in visual functions and in the ability to do two tasks at once |
| 0.05% | Reduced coordination, reduced ability to track moving objects, difficulty steering, slower response to emergencies |
| 0.08% | Poor concentration, short-term memory loss, worse speed control, reduced information processing and perception |
| 0.10% | Reduced ability to keep the vehicle in its lane and to brake appropriately |
| 0.15% | Substantial impairment in vehicle control, attention and processing of what you see and hear |
Notice that real impairment starts well below 0.08%. At 0.05% — Utah's limit — steering, tracking and emergency reactions are already worse. Tired drivers, new drivers and anyone who has also taken medication are affected even more, which is why the safest BAC for driving is zero.
DUI, DWI, OWI: names and penalties
States use different names for the same offense: DUI (driving under the influence) in states such as California and Florida, DWI (driving while intoxicated) in Texas and New York, OVI in Ohio, OWI in states such as Michigan and Iowa, and OUI in Maine and Massachusetts. The core rule is the same: it is illegal to drive while impaired by alcohol or drugs, or with a BAC at or above the legal limit.
Penalties are set by each state and increase sharply for repeat offenses, very high BAC, a child passenger or a crash that injures someone. A first offense commonly brings some combination of:
- License suspension or revocation, often handled separately by the DMV as an administrative action.
- Fines and court costs, plus mandatory alcohol education or treatment programs.
- Possible jail time, which some states make mandatory even for a first offense.
- An ignition interlock device — a breath tester that prevents the car from starting if it detects alcohol. A majority of states require one for all convicted offenders, including first-time offenders.
- Much higher insurance costs and, in many states, proof of financial responsibility (such as an SR-22 filing).
- A criminal record that can affect jobs, school admissions and travel. Repeat DUIs or DUIs causing serious injury are felonies in many states.
Implied consent and chemical tests
Every state has an implied consent law: by driving on public roads, you agree to submit to a chemical test of your breath, blood or urine if an officer lawfully arrests you for impaired driving. Refusing does not make the case go away. In most states it triggers an automatic administrative license suspension, often longer than the suspension for failing the test, and the refusal can be used as evidence in court.
A DUI often creates two separate cases: an administrative case with the DMV about your license, which can move quickly and has short deadlines to request a hearing, and a criminal case in court. Officers may also use field sobriety tests and a preliminary roadside breath test before an arrest; the rules for refusing these vary by state.
Sobriety checkpoints are legal in most states, but a few, such as Texas and Michigan, do not allow them. Wherever you drive, police may stop any driver who shows signs of impairment, such as weaving, drifting, braking erratically or driving without headlights at night.
Under 21: zero tolerance
The legal drinking age is 21 in every state, and every state has a zero-tolerance law for drivers under 21, with a limit of 0.00% to 0.02% depending on the state. Even one drink can put a young driver over it. For a permit holder or a teen with a provisional license, a violation usually means a suspension and can delay the full license by months or years.
Many states also penalize minors for possessing alcohol, using a fake ID or having an open container in the vehicle, and some suspend the license of a minor caught with alcohol even when they were not driving. Expect at least one question about this on the permit test; it is part of every state's handbook. Our graduated driver licensing guide explains how violations affect teen licenses.
Parents and teens should talk about this before the permit, not after a problem. Many families agree on a simple rule: the teen can always call for a ride home, no questions asked that night, rather than drive or ride with someone who has been drinking. If you are getting ready for your permit, our guide on how to get a learner's permit covers the rest of the process.
Drugs, cannabis and medications
Impaired driving laws cover more than alcohol. It is illegal in every state to drive while impaired by any drug: illegal drugs, cannabis — even where it is legal to use — prescription medicines and some over-the-counter products, such as certain antihistamines and sleep aids. A few states set specific legal limits for THC in the blood, while others rely on evidence of impairment.
Read the labels of every medicine you take and ask your doctor or pharmacist whether it is safe to drive. Warnings such as “may cause drowsiness” or “do not operate heavy machinery” apply to driving. Combining alcohol with drugs or medications multiplies the effects, and a driver who has used cannabis and alcohol together is more impaired than with either one alone.
How to avoid impaired driving
Alcohol-impaired driving is involved in roughly 30% of all U.S. traffic deaths, according to NHTSA. Every one of those crashes was preventable. The only safe plan is to decide how you will get home before you start drinking.
- Choose a designated driver who will not drink at all.
- Use a rideshare, a taxi or public transit, or stay where you are.
- Never ride with a driver who has been drinking or using drugs.
- If you host, offer non-alcoholic drinks and food, stop serving well before the end and help guests get home safely.
- If you see a driver who appears impaired, keep your distance, pull over safely and call 911 with the location, direction and vehicle description.
For the permit test, remember the key numbers: 0.08% (Utah 0.05%), 0.04% for commercial drivers, zero tolerance under 21, and that only time lowers BAC. Test yourself with our practice questions by topic.
BAC and DUI FAQ
What is the legal BAC limit in the U.S.?
0.08% for drivers 21 and older in every state except Utah, where it is 0.05%. Commercial drivers are limited to 0.04% and drivers under 21 face zero-tolerance limits of 0.00% to 0.02%.
How many drinks does it take to reach 0.08%?
It depends on body weight, sex, food, time and the drinks themselves. Some people reach 0.08% after two or three standard drinks in an hour. There is no safe number to rely on before driving.
Can you get a DUI under 0.08%?
Yes. If alcohol or drugs impair your driving, you can be arrested and convicted at a lower BAC. Under 21, zero-tolerance limits also apply, and commercial drivers have a 0.04% limit.
What happens if I refuse a breathalyzer?
Under implied consent laws, refusing a chemical test after a lawful DUI arrest usually leads to an automatic license suspension, often longer than for failing, and the refusal can be used in court. Rules for roadside preliminary tests vary by state.
What is the difference between DUI and DWI?
They are mostly different names for the same offense. Some states use DUI, others DWI, OWI, OVI or OUI. A few states use two terms for different levels of impairment, such as New York's DWI and DWAI.
How long does alcohol stay in your system?
Your body eliminates roughly one standard drink per hour, though it varies. After heavy drinking, you can still be over the limit the next morning. Only time lowers BAC.
Is it illegal to drive high on marijuana?
Yes, in every state, even where cannabis is legal. Some states set THC blood limits, and all states prohibit driving while impaired by any drug, including some prescription and over-the-counter medicines.
Official sources
- NHTSA — Drunk driving
- NHTSA — Drug-impaired driving
- IIHS — Alcohol and drugs
- FMCSA — Drug & Alcohol Clearinghouse
- Utah Driver License Division
Keep studying
- Practice tests by topic
- Graduated driver licensing
- CDL general knowledge test
- How to pass the permit test
- Free DMV permit practice test
- Ohio permit test