The blood alcohol level can be calculated based on very simple information, such as the person's weight, gender (man or woman) and the amount of alcohol consumed in a given period of time. The most common formula for calculating BAC in this way is known as the Widmark formula. The amount of alcohol in a drink can vary, this article proposes examples based on the doses considered standard in the United States.
Steps
Part 1 of 2: Calculating the BAC Using Widmark's Formula
Step 1. Find your formula
The simplified version of Widmark's formula is as follows: Blood alcohol rate = [Grams of alcohol ingested / (Body weight in grams xr)] x 100. In this formula, "r" represents the constant of the alcohol distribution in based on gender, which is 0.55 for women and 0.68 for men.
Step 2. Count the number of alcohol you drink
To calculate your blood alcohol level using Widmark's formula, you will need to count how many drinks have been consumed in a given period of time. To be as accurate as possible, the number of drinks counted should be based on standard recipes and doses and not on the number of glasses, bottles or so on. The reason is that the volume and alcohol content of drinks can vary greatly. Standard doses vary from country to country and from drink to drink. For example, in the United States:
- The standard dose of a distillate with an alcohol content of 40%, such as gin or whiskey, is about 45 ml.
- The standard dose of a beer with an alcohol content of 5% is 355 ml.
- The standard dose for a wine with an alcohol content of 12% is 150 ml.
- In the United States, a standard drink contains about 14g of alcohol.
Step 3. Identify the alcohol content
When you know the number of drinks consumed, multiply it by 14 to get the alcohol content in grams. This way you will know how much alcohol is ingested.
- You can also find out how many grams of alcohol were ingested by applying this formula: (Volume of the drink) x (alcohol content of the drink) x 0.789 = grams of alcohol ingested.
- Depending on the doses considered standard in the country where you live, you will have to multiply the number of drinks consumed by the alcohol content in grams.
Step 4. Multiply your body weight by the gender constant
The gender constant is 0.55 for women and 0.68 for men. If you know your weight in pounds only, you can use one of the following formulas to convert it into grams:
- Body weight in pounds / 0.0022046 = body weight in grams.
- Body weight in pounds x 454 = body weight in grams.
- By doing a simple internet search, you can find an online calculator that will help you quickly convert pounds to grams.
Step 5. Divide the grams of alcohol ingested by your body weight in grams multiplied by the gender constant
This calculation will give you the value corresponding to the blood alcohol level.
Step 6. Multiply the resulting value by 100
Take the number you calculated in the previous step and multiply it by 100 to find the alcohol content in the blood expressed as a percentage.
Step 7. Take into account the time spent
If you have been drinking alcohol for any length of time, you will need to take into account the time elapsed and the amount of alcohol your body has already metabolized up to the time you calculated your BAC. To do this, use the following formula:
BAC as a percentage - (time spent in hours x 0, 015)
Part 2 of 2: Practical Example of How to Apply the Widmark Formula
Step 1. Understand the example
Imagine that a woman weighing 120 pounds has ingested 4 drinks of 45ml each of a liqueur with an alcohol content of 40% over the span of 5 hours.
Step 2. Count the number of drinks
In the United States, 4 drinks of 45ml each of a liqueur with an alcohol content of 40% correspond to 4 standard drinks.
Step 3. Identify the alcohol content
Multiply the number of standard drinks in this example (4) by 14 (the alcohol content in grams of a standard drink in the United States) to get the total amount of alcohol, which is 56 grams of alcohol.
Step 4. If necessary, convert your body weight to grams, then multiply it by the gender constant
Continuing with the example, 120 pounds is the equivalent of 54,480 grams (120 pounds x 454 which is the conversion coefficient of pounds to grams). Multiplying the result by the gender constant (in this example 0, 55 being a woman) you will get 29,964.
Step 5. Divide the amount of alcohol ingested in grams by your body weight in grams multiplied by the gender constant
In this example, it is approximately equal to 0.0018689093579 (which is equal to 56 divided by 29,964). You can round the number to 0.00186.
Step 6. Multiply the obtained value by 100 to express it as a percentage
In this example, the value obtained by applying the Widmark formula is 0, 186% (0, 00186 x 100). The multiplication result will reflect the (approximate) BAC as a percentage without taking into account the elapsed time.
Step 7. Include elapsed time in the calculation
In this example, you would first multiply the number of hours spent (5) by 0.015 to get 0.075 and then subtract this number from the percent alcohol value: 0.06 - 0.075 = 0.111. means that the blood alcohol level (approximate) at the end of the 5 hour period will be 0.11%.
Advice
Whether or not you have eaten food before you start drinking will affect your BAC
Warnings
- Widmark's formula is an approximate indicator of the BAC. In most cases, the formula underestimates the amount of alcohol actually present in the blood.
- No blood alcohol formula is as accurate as a blood alcohol test.
- It is never advisable to drive after drinking, regardless of the result you have obtained by applying the Widmark formula.
