How to Calculate Blood Alcohol Content

Blood alcohol content is the measure of alcohol in the blood, usually expressed in a percentage derived from the grams of alcohol per 100 grams of blood. Several numeric conversions are required to determine the amount of alcohol consumed and the amount of blood in the body, so if you'll be driving after drinking it's best to have a device on hand to measure the alcohol level in your breath.

Instructions

Difficulty: Moderate

1. Determine how many drinks the person has imbibed. One drink is equal to a 12 ounce can or bottle of beer, a small glass of wine or a small shot of 100 proof liquor.
2. For a rough estimate, assume that two drinks raise the blood alcohol content by .05 percent.
3. Measure the amount of alcohol you have consumed more accurately by obtaining a measure of how many grams of an alcoholic beverage you have consumed and the proof of the beverage. Proof is twice the percentage of alcohol in a drink, so if you have consumed 10 ounces of 100 proof liquor (10 shots); you have consumed five ounces of alcohol.
4. Convert the ounces of the drink consumed to grams for easier calculation of percentage. Multiply the number of ounces by 28.35 to find the number of grams. If you have consumed five ounces of alcohol, you have consumed 141.75 grams of alcohol.
5. Determine the drinker's weight. Convert pounds to kilograms for easier calculation. Divide the number of pounds by 2.205 to find the number of kilograms. Multiply the kilograms by 1,000 to find the number of grams. For example, a 150 pound person weighs about 68.03 kilograms, or 68,030 grams.
6. Use the drinker's weight in grams to determine the amount of blood in the drinker's body. Men typically have 58 percent blood or water and women have 49 percent blood or water in their body weight. This number may vary, but these are good estimates. For a 150 pound man, multiply 68,030 by .58 to determine that he has 39, 457.4 grams of blood in his body.
7. Divide the grams of alcohol consumed by the grams of blood in the body and multiply by 100 to find the percentage of alcohol in the blood. A 150 pound man who has had 10 shots of 100 proof liquor has roughly a .36 percent blood alcohol content. At this level he has probably blacked out.
8. Realize that your body metabolizes alcohol at a steady rate from your first drink. It is difficult to determine how quickly an individual metabolizes alcohol because individual body fat percentages and metabolic rates differ. However, you can estimate that a person will metabolize about .015 percent per hour.