In 49 U.S. states and Washington, D.C., a blood alcohol concentration (BAC) of 0.08% or higher legally means you are driving under the influence. Utah is the exception, with a lower limit of 0.05%. These are “per se” limits, meaning no additional proof of impairment is needed. If a chemical test shows you at or above the threshold, that alone is sufficient for a DUI charge.
The 0.08% Standard and Utah’s Lower Limit
The 0.08% BAC limit became universal across the U.S. after Congress tied federal highway funding to its adoption starting in 2004. Every state eventually complied. Then in 2017, Utah passed a law lowering its limit to 0.05%, which took effect in December 2018. Utah became the first and, as of 2025, only state to make this change. The National Transportation Safety Board has recommended that other states follow Utah’s lead, viewing the lower limit as a deterrent that discourages people from driving after drinking at all.
Lower Limits for Commercial and Underage Drivers
The standard 0.08% (or 0.05% in Utah) applies to adults driving personal vehicles. Two groups face much stricter thresholds.
Commercial vehicle operators are held to a federal limit of 0.04%. This applies regardless of whether the driver is on or off duty at the time. A conviction above 0.04% results in disqualification from holding a commercial driver’s license.
Drivers under 21 fall under zero-tolerance laws in every state. These laws set a maximum BAC below 0.02%, and in many states the effective limit is 0.00%. Even a single drink can put an underage driver over the legal threshold.
Per Se vs. Impairment Charges
There are actually two types of DUI offenses, and understanding the difference matters. A “per se” DUI is based entirely on your BAC reading. No one needs to prove you were swerving or slurring your words. The number alone is the crime.
A “generic” or impairment-based DUI, on the other hand, is about how alcohol affected your ability to drive. Under this standard, a person is considered under the influence if their mental or physical abilities are so impaired that they can no longer drive with the caution of a sober person. This means you can be charged with a DUI even if your BAC is below 0.08%. If an officer observes impaired driving and field sobriety tests support that observation, the charge can stick regardless of the number on the test.
What Impairment Actually Looks Like at Each Level
Alcohol doesn’t wait until 0.08% to affect your brain and body. Measurable impairment begins well below the legal limit, which is part of why some safety advocates push for lower thresholds.
At 0.02%, most people feel relaxed and slightly warm. Judgment starts to shift, and the ability to track a moving object or handle two tasks at once declines. You might not feel impaired at all, but your visual processing is already slower than normal.
At 0.05%, the effects become more noticeable. Coordination drops, alertness decreases, and inhibitions loosen. In driving terms, this translates to difficulty steering and slower responses to emergency situations. This is the level where Utah draws its legal line.
At 0.08%, the legal limit in most states, muscle coordination is clearly affected. Balance, speech, vision, reaction time, and hearing all suffer. Short-term memory weakens, concentration narrows, and it becomes harder to detect danger. Speed control deteriorates, and the brain processes visual information more slowly.
At 0.15%, nearly double the standard legal limit, muscle control is severely reduced. Balance is significantly impaired, and vomiting is common unless the person has built up a high tolerance. Driving ability at this level is substantially compromised across nearly every measure.
Why BAC Varies So Much Between People
Two people can drink the same amount and end up with very different BAC readings. The biggest factors are body weight, sex, and body composition. Alcohol distributes through the water in your body, so people with more body fat and less water (per pound) reach higher BAC levels from the same amount of alcohol. Women generally have a higher proportion of body fat relative to water than men of the same weight, which is why women typically reach a higher BAC from an equivalent number of drinks.
The rate at which your body eliminates alcohol is also important. On average, a 154-pound person metabolizes about 7 grams of alcohol per hour, roughly equivalent to one standard drink. That rate doesn’t change much regardless of how much coffee you drink or how much food you eat after drinking. Food eaten before or during drinking can slow absorption, but once alcohol is in your bloodstream, your liver clears it at a relatively fixed pace.
How BAC Is Measured
Law enforcement uses two primary methods: breath tests and blood draws. Roadside breath tests give a quick estimate, while evidentiary breath or blood tests performed at a station or hospital carry legal weight.
Breath tests tend to read slightly lower than blood tests. In one study of over 400 paired samples, breathalyzer results came in lower than blood results by more than 0.01% about 61% of the time, matched within 0.01% about 33% of the time, and read higher only 6% of the time. This margin matters because it means a breath test reading of 0.08% could correspond to a somewhat higher actual blood alcohol level. Defense attorneys sometimes challenge breath test accuracy on these grounds, but courts generally accept both methods as valid evidence.