What Is BAC?

BAC stands for Blood Alcohol Concentration, a measure of how much alcohol a person has in their system. BAC is measured in grams of alcohol/milliliter of blood.

Why Is BAC Used to Measure Intoxication?

Any alcohol you drink ultimately ends up in your blood. As you consume it, your body absorbs alcohol into the blood through the stomach lining and the small intestine. This is a gradual process, and alcohol takes time to be absorbed. As more of it gets into your blood, more of it reaches your brain and you become more impaired.

BAC (“blood alcohol concentration” or “blood alcohol content”) is a way of measuring how much alcohol you have in your system. It’s widely used by courts to draw the line between “intoxicated” and “sober,” but it is not a perfect metric.

breath test to measure bac

A breath test to measure BAC. Blood Alcohol Measurements tell the state of your BAC if you’re too intoxicated to drive.

Why Does BAC Vary From Person to Person?

Two different individuals can drink the same amount of alcohol and end up with a different BAC. The difference depends on:

  • Your age and weight
  • How much food you consumed
  • What type of alcohol you drank
  • Whether it was carbonated
  • How long you took to drink it

Despite these differences in alcohol consumption, if two people have the same BAC, they will experience roughly the same level of impairment or intoxication. Therefore, it’s used as a standard in DUI cases.

Alcohol tolerance can also make it difficult to know how much you’ve been drinking. People who drink regularly can ingest more alcohol before they feel impaired. For the law, how you feel does not matter. It’s how you act and what your BAC level is.

How Is BAC Measured?

BAC is normally expressed as a percentage. For example, the legal “limit” for most drivers in California is 0.08% BAC, although sometimes, a much lower BAC will still count as a DUI. BAC percentages are really grams of alcohol per milliliter of blood, which you may see in a test report, but the units are equivalent to make a percentage.

There are two primary ways the police may measure your BAC. At the scene of the stop, they may use a breath test with a breathalyzer machine. If they take you to the station or a hospital, they can also do a blood test.

BAC can be misleading, even when confirmed with a test. Often, BAC will continue to rise long after you stopped drinking because you haven’t absorbed all the alcohol yet. That means you were less drunk when you were pulled over than you were hours later at the breath test. In some cases, a rising BAC defense is valid for DUI charges.

Why Would I Be Charged With DUI Even With a Low BAC?

A DUI is really about getting drivers too unsafe to drive off the road. Under California law, if you have a BAC of 0.08% or higher, you are intoxicated even if you were driving perfectly. That’s the line the law has set for intoxication under any circumstances, even if your alcohol tolerance is high.

However, if you are driving unsafely and the police can find a little alcohol in your system through a BAC test, they can try to pin your unsafe driving on your alcohol consumption. They may not even need the test if there is other evidence of drinking or drug use.

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