How to Calculate Your Estimated Blood Alcohol Content

Written by nancy kerstetter
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How to Calculate Your Estimated Blood Alcohol Content
One drink has the capability to impair your judgement. (alcoholic drink image by Horticulture from Fotolia.com)

Blood Alcohol Concentration (BAC) is used by law enforcement officials to determine if a driver is intoxicated. BAC is the percentage of alcohol present in the person's blood. The legally allowed percentage varies from state to state but is generally below .08 per cent. Many factors contribute to BAC such as body size, gender, general health, amount of food in your stomach, percentage of body fat and type of alcohol consumed. You can use an equation to approximate the amount of alcohol in your blood, however, the best plan is to have a non-drinking friend drive, or call a cab.

Skill level:
Easy

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Instructions

  1. 1

    Use this equation to determine your BAC: (A x 5.14/Weight x Gender) - (.015 x H) = BAC per cent. Determine the amount of alcohol consumed by estimating the total number of ounces drank. Multiply the total number of ounces times the amount of alcohol in the beverage. Beer is usually 354ml per serving, wine is 177 - 296ml, champagne is 118-177ml, shots are 44.4ml and mixed drinks contain 59.1ml of alcohol. Beer is 3-7 per cent alcohol, liquor is 30-50 per cent alcohol, wine is 12-21 per cent alcohol and champagne is 15-20 per cent alcohol. For instance, if you drink two beers (354ml each, alcohol 5 per cent) and two shots (44.4ml each, 40 per cent alcohol) your consumption is (24 X .05) + (3 X .40) = 2.4. This number represents "A" in the equation.

  2. 2

    Take your weight in pounds and multiply it by .73 if a male, .66 if a female. Divide this number into 5.14. Take this number and multiply it by "A", the number of ounces of alcohol consumed factored with alcohol percentage from Step 1. Save this number for Step 4. To continue the example, take your weight of 160 and multiply it by .73, the male factor, 160 X .73 = 116.8. Now, 5.14 divided by 116.8 = .044. Next, multiply by "A". Compute the equation: 2.4 X .044 = .1056.

  3. 3

    Multiply .015 times the number of hours passing since starting to consume alcohol. The .015 figure is the average alcohol elimination rate reflecting the time needed to recover from the alcohol in your bloodstream. In the example, you have been drinking for two hours, 2 X .015 = .03.

  4. 4

    Subtract the time factor (Step 3) from the number calculated in Step 2 which are the consumption, weight, gender factors. This total will give you a general idea of BAC. In the example .1056 - .03 = .0756. Your BAC is .0756%. Your BAC is barely within the allowable tolerance for driving. You are alcohol-impaired. Driving would be dangerous for you. You should have someone sober drive you home.

Tips and warnings

  • Plan ahead; enlist a sober friend to drive you home if you want to drink alcohol.
  • Eat a full meal before imbibing alcohol. When you have food in your stomach, alcohol enters your bloodstream more slowly, but it still affects your BAC.
  • Alcohol mixed with fruit or water absorbs more slowly than alcohol mixed with carbonated beverages.
  • Your emotional and physical condition and health affect your actual BAC. Other factors affecting your BAC include what you have eaten, medication ingested or other drugs used. Some 17 states require BAC testing for all drivers involved in serious injury crashes. Hawaii and Connecticut have the highest number of drunk driver-related traffic deaths per capita in the country. Utah has the lowest number.

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