Blood Alcohol Content (BAC) Calculator

How to Calculate Blood Alcohol Content (BAC)

Blood Alcohol Content (BAC) is a measure of the amount of alcohol in your bloodstream. Understanding how to calculate BAC can help you make informed decisions about alcohol consumption and its effects on your body.

BAC Formula

The formula used to calculate BAC is:

$$BAC = \frac{0.806 \times \text{drinks} \times 1.2}{\text{weight} \times r} - (0.015 \times \text{hours})$$

Where:

• BAC is Blood Alcohol Content
• 0.806 is a constant for body water in the blood (80.6% of blood is water)
• drinks is the number of standard drinks consumed
• 1.2 is the amount of pure alcohol in ounces in a standard drink
• weight is body weight in kilograms
• r is the alcohol distribution ratio:
  • 0.68 for males
  • 0.55 for females
• 0.015 is the average rate at which alcohol is metabolized per hour
• hours is the number of hours since the first drink

Calculation Steps

1. Determine the number of standard drinks consumed
2. Convert body weight to kilograms if necessary
3. Choose the appropriate alcohol distribution ratio based on gender
4. Calculate the alcohol concentration: (0.806 × drinks × 1.2) / (weight × r)
5. Subtract the amount of alcohol metabolized: 0.015 × hours
6. The result is the estimated BAC

Example Calculation

Let's calculate the BAC for a male who weighs 80 kg, has consumed 3 drinks over 2 hours:

Step 1: Apply the formula

$$\begin{align} BAC &= \frac{0.806 \times 3 \times 1.2}{80 \times 0.68} - (0.015 \times 2) \\ &= \frac{2.8996}{54.4} - 0.03 \end{align}$$

Step 2: Calculate

$$\begin{align} BAC &= 0.0533 - 0.03 \\ &= 0.0233 \end{align}$$

Step 3: Final result

The estimated BAC is 0.0233 or about 0.02%.

Visual Representation

This bar chart illustrates the calculated BAC (0.0233) in comparison to the legal limit in most countries (0.08) and the level at which impairment begins (0.04).