In 49 U.S. states, the legal limit for alcohol while driving is a blood alcohol concentration (BAC) of 0.08%. Utah is the exception, with a lower limit of 0.05% that took effect in December 2018. Any BAC at or above these thresholds is considered “per se” illegal, meaning you can be charged regardless of whether you appear impaired.
What BAC Actually Measures
BAC represents the percentage of alcohol in your bloodstream by weight. A BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood. At that level, you typically experience reduced muscle coordination, impaired judgment and reasoning, and difficulty detecting danger. These effects are why 0.08% became the national standard, though the National Transportation Safety Board has recommended since 2013 that all states lower the limit to 0.05%, arguing that 0.08% is too high. As of late 2024, only Utah has followed that recommendation.
Lower Limits for Commercial Drivers and Minors
Not everyone is held to the 0.08% standard. Commercial vehicle operators, including truck and bus drivers, face a federal limit of 0.04% BAC. This applies whether they’re on duty or off duty at the time of the stop. A conviction at that level results in disqualification from operating a commercial vehicle.
Drivers under 21 are subject to zero-tolerance laws in every state. The exact threshold varies, but most states set it between 0.00% and 0.02%. In New York, for example, a driver under 21 can be charged with a BAC as low as 0.02%.
How Many Drinks It Takes to Reach 0.08%
The number of drinks that push you over the limit depends on your body weight, biological sex, how quickly you’re drinking, and whether you’ve eaten. A “standard drink” is 12 ounces of beer, 5 ounces of wine, or 1 ounce of liquor.
For men, the numbers look roughly like this: a 130-pound man can reach 0.08% after just three drinks in one hour. A 160-pound man typically needs about four drinks over two hours to hit the same level. Women generally reach 0.08% faster because of differences in body composition and how alcohol is distributed. A 100-pound woman can reach the legal limit after only two drinks in one hour, while a 160-pound woman may reach it after three drinks in the same timeframe.
These are estimates, not guarantees. Food in your stomach, medications, fatigue, and individual metabolism all shift the numbers. The only way to know your BAC with certainty is to measure it.
How Long Alcohol Takes to Leave Your System
Your body clears alcohol at a relatively fixed rate: roughly one standard drink per hour for someone weighing about 155 pounds. That translates to a BAC drop of approximately 0.015% per hour. So if you stop drinking at a BAC of 0.08%, it would take a little over five hours to return to 0.00%. Coffee, water, food, and cold showers don’t speed this up. Only time works.
This matters for morning-after driving. If you were drinking heavily and went to sleep at midnight with a BAC of 0.15%, you could still be over the legal limit at 7 a.m.
How BAC Is Tested
Law enforcement primarily uses two methods: breath tests and blood draws. Breathalyzers are the most common roadside tool, but they tend to read slightly lower than actual blood alcohol levels. One study comparing the two methods found that breathalyzer results came in lower than the blood test 61% of the time, matched within a narrow margin 33% of the time, and read higher only 6% of the time. Blood tests are considered the gold standard for accuracy and are typically used as the official evidentiary test after an arrest.
Urine tests exist but are less commonly used for legal proceedings because alcohol concentration in urine doesn’t map as reliably to impairment levels.
DUI, DWI, and Other Charges
The terminology for alcohol-related driving offenses varies by state. DUI (driving under the influence) and DWI (driving while intoxicated) are the most common terms, but some states use OUI (operating under the influence), OWI (operating while intoxicated), or DWAI (driving while ability impaired). In practice, these labels often describe the same basic offense. Some states use different terms to distinguish severity: New York, for instance, uses DWAI for BAC levels between 0.05% and 0.07%, reserving DWI for 0.08% and above.
Importantly, you can be charged below 0.08% in any state if an officer determines you’re visibly impaired. The per se limit means automatic illegality at that number, but impaired driving is illegal at any BAC.
How U.S. Limits Compare Internationally
The U.S. standard of 0.08% is among the highest in the developed world. Most of Europe sets the limit at 0.05% (equivalent to the U.S. measurement of 0.05%), including France, Germany, Italy, Austria, and Spain. Several countries go even lower: Sweden, Norway, and Poland set theirs at 0.02%. The Czech Republic, Hungary, Romania, and Slovakia enforce a true zero-tolerance policy of 0.00% for all drivers.
The UK is the notable European outlier, with a limit of 0.08%, matching most U.S. states. Scotland, however, broke from the rest of the UK in 2014 and lowered its limit to 0.05%. Many European countries also impose stricter limits on commercial and novice drivers, often 0.00% to 0.02%, regardless of the standard limit.