The alcohol a person drinks is absorbed by the body and eventually ends up in the bloodstream. The amount of alcohol in a person's bloodstream—measured as blood alcohol concentration (BAC)—is directly related to his or her level of impairment. Because of this relationship between BAC and impairment, all states make it illegal to drive if your BAC exceeds a certain level.
Below is a BAC chart that can give you a rough idea of what your BAC might be after a certain number of drinks. However, everyone metabolizes alcohol differently and there are lots of factors that can affect the rate at which this happens. So, while this table can give you an estimate of BAC, a direct measurement is the only way to be reasonably sure of how much alcohol you have in your system. In other words, don't rely on this chart to determine when you're safe to drive—if you've been drinking alcohol or using any other intoxicating substances, don't get behind the wheel.
This chart (which is based on the chart published by the California Department of Motor Vehicles) shows estimated BAC levels based on the number of drinks consumed and the person's sex and weight. You'll note at the bottom it says to subtract a certain amount from the BAC for every 40 minutes that has lapsed between drinks. The subtraction is to compensate for the metabolization that occurs after you consume alcohol. In other words, after the alcohol is absorbed into your system, it starts to dissipate, and your BAC drops.
Number of Drinks |
Body Weight in Pounds |
Driving Condition |
||||||||
100 |
120 |
140 |
160 |
180 |
200 |
220 |
240 |
|
||
0 |
M |
.00% |
.00% |
.00% |
.00% |
.00% |
.00% |
.00% |
.00% |
Safe to Drive |
W |
.00% |
.00% |
.00% |
.00% |
.00% |
.00% |
.00% |
.00% |
||
1 |
M |
.06% |
.05% |
.04% |
.04% |
.03% |
.03% |
.03% |
.02% |
Impaired |
W |
.07% |
.06% |
.05% |
.04% |
.04% |
.03% |
.03% |
.03% |
||
2 |
M |
.12% |
.10% |
.09% |
.07% |
.07% |
.06% |
.05% |
.05% |
|
W |
.13% |
.11% |
.09% |
.08% |
.07% |
.07% |
.06% |
.06% |
||
3 |
M |
.18% |
.15% |
.13%% |
.11% |
.10% |
.09% |
.08% |
.07% |
|
W |
.20% |
.17% |
.14% |
.12% |
.11% |
.10% |
.09% |
.08% |
Above the Legal Limit |
|
4 |
M |
.24% |
.20% |
.17% |
.15% |
.13% |
.12% |
.11% |
.10% |
|
W |
.26% |
.22% |
.19% |
.17% |
.15% |
.13% |
.12% |
.11% |
||
5 |
M |
.30% |
.25% |
.21% |
.19% |
.17% |
.15% |
.14% |
.12% |
|
W |
.33% |
.28% |
.24% |
.21% |
.18% |
.17% |
.15% |
.14% |
||
Subtract .01% for every 40 minutes that lapse between drinks. One drink equals 1.5 ounces of 80 proof liquor, 12 ounces of 5% beer, or 5 ounces of 12% wine. |
In almost every state, you can get a DUI for operating a vehicle with a BAC of .08% or more. (Utah goes a little further by setting the legal limit at .05%.)
However, these BAC limits are for drivers who are at least 21 years old. For underage drivers, the limits are much lower. Depending on the state, the legal limit for drivers who are younger than 21 years old might be .01%, .02%, .03%, or any measurable amount of alcohol.
Many states also impose more severe penalties in DUI cases where the BAC is especially high. For instance, some states (like Arizona and Alabama) punish DUI convictions more harshly when the driver's BAC is .15% or more.