BAC stands for blood alcohol concentration. Here is what the numbers do
The percentage is the weight of alcohol in a volume of blood: 0.08% is 0.08 grams per deciliter. What matters is not the arithmetic but the fact that impairment starts well below every legal line in the country — and that only one level guarantees safe driving.
0.00% is the only BAC at which safe driving can be guaranteed
Federal data records over two thousand deaths a year in crashes where a driver measured between 0.01 and 0.07 — legal everywhere, impaired anyway. The legal limit marks where the number alone proves an offense, not where risk begins.
Source: NHTSA, Drunk Driving: The Effects of Blood Alcohol Concentration, checked 2026-08-30
What each BAC level does to a driver
Two columns matter: what the level does to the body, and what it does behind the wheel. The second is what an officer observes before any machine is involved.
| BAC level | Typical effects | Effects on driving |
|---|---|---|
| 0.02% | Some loss of judgment, relaxation, slight body warmth, altered mood. | Decline in visual function and in the ability to do two things at once. |
| 0.05% | Exaggerated behavior, loss of small-muscle control such as focusing your eyes, lowered alertness. | Reduced coordination and slower response to emergencies. Colorado charges DWAI from here. |
| 0.08% | Poor muscle coordination, harder to detect danger, impaired judgment, self-control and memory. | The per se limit in every state but Utah: at this reading the number alone proves the offense. |
| 0.15% | Far less muscle control than normal, vomiting may occur, major loss of balance. | Substantial impairment in vehicle control and in attention to the driving task. Many states add penalties from this level. |
People often describe readings as multiples of the limit: twice over is 0.16%, three times over the legal limit of alcohol is 0.24%. At those levels several states stop treating it as an ordinary charge — Arizona calls 0.20% and above Super Extreme DUI and attaches 45 days of jail that cannot be suspended.
Source: NHTSA, Drunk Driving: The Effects of Blood Alcohol Concentration, checked 2026-08-30
What counts as over, and for whom
| Who | Limit | What it means |
|---|---|---|
| Every state except Utah | 0.08% | The per se limit for drivers 21 and over: at or above it the number alone proves the offense, with no argument about how you were driving. source |
| Utah | 0.05% | Utah lowered its per se limit from 0.08% to 0.05% under House Bill 155, in force since 30 December 2018, and remains the only state at that level. source |
| Colorado, lesser charge | 0.05% | Colorado keeps DUI at 0.08% but charges DWAI from 0.05%, so the range between the two is not a safe zone — it is its own offense. source |
| New York, lesser charge | over 0.05% to 0.07% | DWAI sits below the 0.08% DWI line. A first DWAI is a traffic infraction with a 90-day suspension, against a minimum six-month revocation for DWI. source |
| Commercial drivers | 0.04% | Half the ordinary limit, and it applies while operating a commercial vehicle regardless of what the personal license allows. source |
| Drivers under 21 | any detectable amount, in most states | Zero-tolerance rules run alongside the adult limit. Wisconsin requires absolute sobriety under 21; New York and Colorado set the line at 0.02%. source |
Estimating where you would land
Use this to understand the scale of what you drank, not to decide anything. The estimate is a range because bodies differ, and even a low range is not permission.
How long does alcohol take to hit? Immediately — it moves from the stomach and intestines into the bloodstream within minutes, faster on an empty stomach. And because absorption outruns metabolism, the number can still be climbing after your last drink.
How long until it clears? Only time does that, at a rate your liver sets. Nothing on this page or anywhere else speeds it up.
Rough estimate, not a green light
This works out where the Widmark formula would put you. It cannot account for what you ate, what you take, how fast you drank or how your liver works, and the spread between two people with identical inputs is wide.
What is actually happening in your body
Nothing speeds it up
The body starts metabolizing alcohol within seconds and continues at a steady rate — regardless of how much was drunk, and regardless of attempts to sober up with coffee or by other means. Cold showers, food and fresh air change how awake you feel, not what a test measures.
Source: NIAAA, The Basics: Defining How Much Alcohol is Too Much, checked 2026-08-30
It arrives faster than it leaves
Alcohol is absorbed into the bloodstream far faster than it is metabolized, so the concentration keeps building when you drink again before the previous drink has been processed. That is why a reading can still be rising after the last glass.
Source: NIAAA, The Basics: Defining How Much Alcohol is Too Much, checked 2026-08-30
Four or five drinks reach the limit
A typical adult reaches 0.08% — the legal limit in every state but Utah — after about four drinks for women or five for men, in roughly two hours. Body size, genetics and liver function move the number, but not the direction.
Source: NIAAA, The Basics: Defining How Much Alcohol is Too Much, checked 2026-08-30
The liver does almost all of it
Alcohol dehydrogenase in the liver turns ethanol into acetaldehyde, which a second enzyme converts to acetate and finally to water and carbon dioxide. The rate is set by your enzymes, not by your intentions — and liver damage slows it further.
Source: NIAAA, Alcohol Metabolism, checked 2026-08-30
BAC questions
What does BAC stand for?
Blood alcohol concentration. It is the weight of alcohol in a given volume of blood, written as a percentage: 0.08% means 0.08 grams of alcohol per deciliter of blood. Breath machines do not measure blood at all — they measure alcohol in exhaled air and convert it using a fixed ratio.
This is the only BAC level at which safe driving can be guaranteed
0.00%. That is the answer on driver education tests, and it is not a formality: federal data records more than two thousand deaths a year in crashes where a driver was between 0.01 and 0.07 — below every legal limit in the country. Impairment starts before illegality does.
What is the legal limit for alcohol?
0.08% for drivers 21 and over in every state except Utah, which lowered its limit to 0.05% at the end of 2018. Commercial drivers are held to 0.04%, and drivers under 21 face zero-tolerance rules that start at any detectable amount in most states.
How long does it take for alcohol to hit?
It begins immediately — alcohol passes from the stomach and intestines into the bloodstream and starts affecting the brain within minutes. Drinking on an empty stomach speeds that up and produces a higher peak. Because absorption outruns metabolism, your reading can keep climbing after you have stopped drinking.
How accurate is a BAC calculator?
It is an estimate of an average body, not a measurement of yours. The Widmark formula uses weight, body composition and time, and cannot account for food, medication, genetics or how quickly you drank. Two people with identical inputs can differ substantially, which is why the estimate here is shown as a range and why no calculator should ever be used to decide whether to drive.
How the breath test works and what refusing costs → DUI, DWI, OWI explained →
Attorney advertising. InterlockDeviceNearMe is not a law firm, does not practice law, and does not give legal advice. Nothing here creates an attorney-client relationship. Requesting a consultation connects you with an independent attorney or a legal referral service, who decide separately whether to take your case. Case outcomes depend on facts we do not know, and no result is ever promised. Deadlines in DUI cases are short and vary by state — speak to a licensed attorney in your state before relying on anything you read here.