The Law Dictionary

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How To Calculate BAC

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As the best judges will remind you, driving after drinking is not illegal; driving impaired is illegal. When you are enjoying yourself, make sure you know when you have reached your limit. Here is how to calculate blood alcohol level, commonly known as BAC.

How much beer, wine or liquor can I enjoy?

Some people want to know how many drinks they can consume each hour, but it is rather difficult to calculate this. Light beers might have about 4% to 9% alcohol content with heavier craft beers having about 9% to 12% alcohol content. Wine has a wide range from white 4% or so up to port at 20%. Liquor is from 33% and upwards.

Your blood alcohol content is the percentage of your blood consisting of alcohol. When you drink, the alcohol goes quickly into your bloodstream leading to your “buzz.” This also can immediately impair your:

  • Sight
  • Motor skills
  • Thought process

The rate at which someone becomes impaired or drunken is based on gender, age, body size, food in the stomach, ethnicity, and many other factors. Certain people will not be as affected by alcohol as quickly, but all must remember that law enforcement is looking at the percentage of alcohol still in your bloodstream. Each state has its own regulations for which BAC level is acceptable.

Measuring Alcohol in Blood

The original breathalyzer was invented back in 1954 using chemical oxidation and light to measure alcohol presence. Since then the technology has been upgraded tremendously. If a police officer believes that you are under the influence of alcohol or drugs, he will give you a breathalyzer on the site. This handheld model uses electrochemical platinum fuel cells technology to measure the alcohol in your breath.

For court proceedings, the most accurate readings are preferred. Police officers taking you into custody might request that you offer a blood sample back at the station. The near-infrared spectrophotometer technology is the most accurate, but all equipment has its own error range.

The BAC measures the parts of blood, which consist of alcohol. You have heard of readings, like 0.04 and 0.08, all of these are less than 1% of your blood. For example, if you blow a BAC of 0.04, it means you have 4 parts (grams) alcohol for every 10,000 parts (grams) blood. It seems rather small, but it can easily impair your senses.