Lots of factors affect blood alcohol concentration (BAC), and a person's BAC is generally always in a state of rising or falling. However, the most influential considerations include:

• number of drinks
• sex
• body weight, and
• amount of time spent drinking.

Estimating BAC: Limitations

The chart below provides only an estimate of what a person’s BAC might be. You shouldn’t rely on the accuracy of this estimate in making decisions like whether to drive.

There are lots of factors the chart doesn’t account for that can affect BAC or how “impaired” someone is. The chart doesn’t address, for instance, food eaten, medications taken, or amount of sleep.

Everyone absorbs and metabolizes alcohol at different rates. And you should know that you can be arrested for and convicted of a DUI for driving while impaired by alcohol or drugs—even if your BAC is under the legal limit.

If you’ve been drinking—regardless of how much—it’s best not to get behind the wheel.

How to Use the Chart

In all 50 states, it’s illegal to drive with a BAC of .08% or more—a “per se” DUI. (The BAC limit is often lower for drivers under 21 and commercial vehicle drivers.) The chart below gives BAC estimates based on sex, number of drinks of specific sizes and alcohol content, and body weight. (It’s based on a similar chart found in the California Driver Handbook.)

To estimate a person’s BAC:

1. Find the BAC value corresponding to the person’s sex, body weight, and number of drinks consumed.
2. Subtract .01% from the BAC for every 40 minutes that have passed since the person started drinking.

For example, suppose a 120-pound woman had three glasses of wine in 80 minutes. From the chart, the BAC would be .17%. But because 80 minutes have passed, we need to subtract .02% (.01% for each 40 minutes). The woman’s estimated BAC would then be .15%.