No fixed number of drinks equals 0.08, in Montana or anywhere else. Montana's DUI statute does not mention drinks. It asks whether your ability to drive safely was diminished, or whether a test of your breath, blood, or oral fluid showed an alcohol concentration at or above a set level (MCA § 61-8-1002). This page explains why drink-count rules fail and what the law tests for. It is part of our Montana DUI Guide.
What the Law Tests
There are two ways the State can prove an alcohol DUI. One is impairment: you drove, or were in actual physical control of, a vehicle while under the influence, which Montana defines as a diminished ability to safely operate a vehicle (MCA §§ 61-8-1002(1)(a), 61-1-101). The other is a number: an alcohol concentration of 0.08 or more, 0.04 or more in a commercial motor vehicle, or 0.02 or more for a driver under 21 (MCA § 61-8-1002(1)(b), (c), (e)).
Neither test asks how many drinks you had. An officer will ask, and your answer becomes evidence, but the charge rests on the driving, the officer's observations, and the test result. Our page on per se and impairment DUI compares the two theories.
Five Things That Change the Result
NHTSA's public guide, The ABCs of BAC, lists the factors that determine how high a person's alcohol concentration rises:
| Factor | What NHTSA says |
|---|---|
| How much you drink | The more you drink, the higher the alcohol concentration. |
| How fast you drink | Alcohol consumed quickly produces a higher peak than the same amount spread over a longer time. |
| Sex | Women generally have less body water per pound than men, so more alcohol stays in the blood. |
| Body weight | A heavier person has more body water to dilute the alcohol. |
| Food in the stomach | Absorption is slower if you have eaten. |
The same guide adds that "because of the multitude of factors that affect BAC, it is very difficult to assess your own BAC or impairment." A chart can hold one or two of those factors steady. It cannot account for all five, and it knows nothing about the night you actually had.
A Drink Is Not a Fixed Amount
Drink charts assume a "standard drink." The National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines that as about 14 grams, or 0.6 fluid ounces, of pure alcohol. Its examples are a 12-ounce regular beer at 5 percent alcohol, a 5-ounce glass of wine at 12 percent, or a 1.5-ounce shot of 40 percent spirits.
Real drinks often do not match. NIAAA's own example is that a 12-ounce beer at 10 percent alcohol contains two standard drinks. A pint is larger than 12 ounces, a restaurant wine pour may be larger than 5 ounces, and a mixed drink may hold more than one shot. A person who honestly reports "two beers" may have had considerably more alcohol than a chart assumes.
Timing Matters as Much as Quantity
Alcohol concentration is not a fixed fact about an evening. It rises while alcohol is being absorbed and falls as the body eliminates it. NHTSA says alcohol can be measured in the blood within 30 to 70 minutes after a drink. Food slows absorption, and a level can still be rising after the last drink. That is why two people who drank the same amount can test differently, and why a test taken at the station does not always match the level at the wheel. See rising alcohol levels.
Impairment Starts Before 0.08
The 0.08 limit is a legal line, not the point where alcohol begins to affect driving. NHTSA's guide lists a decline in visual function and in the ability to do two tasks at once at 0.02, and reduced coordination and difficulty steering at 0.05. Its officer training manual puts it this way: there is no simple answer to how much a person can drink before becoming impaired, "except to say that any amount of alcohol will affect a person's ability to drive to some degree."
Montana's statute reflects that. A result above 0.04 and below 0.08 creates no inference either way, and it "may be considered with other competent evidence" of guilt or innocence (MCA § 61-8-1002(2)(b)).
Why We Do Not Publish a Chart
A table that says a person of a given weight can have a given number of drinks invites people to drink up to a line that does not exist. It would be wrong for many readers, and it would say nothing about impairment, which is the charge an officer can bring at any level. The only amount that carries no DUI risk is none before driving. That is not a moral judgment. It is what the statute and the science add up to.
If You Have Already Been Charged
After an arrest, the question is no longer how many drinks you had. It is whether the stop was lawful, how the tests were given, and whether the instrument and the operator met Montana's requirements. Our pages on how alcohol concentration is measured and DUI defenses explain where those questions are asked. If this is a first charge, see first-offense DUI in Montana.
This page explains Montana law in general as of the 2025 Montana Code Annotated. The alcohol information comes from NHTSA (The ABCs of BAC, DOT HS 809 844, and its DWI Detection and Standardized Field Sobriety Testing manual) and NIAAA. It is not legal or medical advice about your specific situation.