Blood Alcohol Content (BAC) is a measure of the amount of alcohol in a person's bloodstream. It is expressed as a percentage. For example, a BAC of 0.08 means that there are 0.08 grams of alcohol for every 100 milliliters of blood. Driving with a BAC at or above 0.08% is illegal in all US states.
This calculator provides an *estimation* of your BAC based on common formulas. It's important to understand that individual BAC can vary significantly due to factors like metabolism, food intake, hydration, medication, and genetics.
How is BAC Calculated?
The Widmark formula is a commonly used method to estimate BAC. A simplified version for personal calculators often looks like this:
BAC = (A / (W * r)) * 100
Where:
A = Total grams of alcohol consumed. This is calculated by: (Number of Standard Drinks) * (Average grams of alcohol per standard drink). A standard drink in the US contains approximately 14 grams of pure alcohol.
W = Body weight in kilograms. If weight is in pounds, divide by 2.205 to convert to kilograms.
r = The Widmark factor, which is the distribution ratio of alcohol in the body. This factor is generally:
0.68 for males
0.55 for females
This difference accounts for variations in body water content between genders.
This initial calculation gives the peak BAC. Alcohol is metabolized over time. A common metabolic rate is approximately 0.015% per hour. Therefore, to estimate BAC after a certain time:
*Note: This example uses simplified values. Actual BAC can differ.*
Important Considerations:
Standard Drink Definition: The calculator assumes a standard drink contains 14 grams of pure alcohol (e.g., 12 oz beer, 5 oz wine, 1.5 oz spirits).
Metabolism Rate: The 0.015% per hour is an average. Your personal rate may be faster or slower.
Food Intake: Drinking on an empty stomach leads to faster alcohol absorption and higher BAC.
Medications and Health: Certain medications and health conditions can affect alcohol metabolism.
Hydration: Dehydration can concentrate alcohol in the bloodstream.
Legal Limits: BAC limits vary by jurisdiction. In many places, 0.08% is the legal limit for driving.
Disclaimer: This calculator is for informational purposes only and should not be used as a substitute for professional judgment or legal advice. Never drink and drive. If you have consumed alcohol, arrange for a safe ride home.
function calculateBAC() {
var weightInput = document.getElementById("weight");
var weightUnitSelect = document.getElementById("weightUnit");
var genderSelect = document.getElementById("gender");
var drinksInput = document.getElementById("drinks");
var hoursInput = document.getElementById("hours");
var weight = parseFloat(weightInput.value);
var weightUnit = weightUnitSelect.value;
var gender = genderSelect.value;
var drinks = parseFloat(drinksInput.value);
var hours = parseFloat(hoursInput.value);
var bacValueElement = document.getElementById("bacValue");
if (isNaN(weight) || isNaN(drinks) || isNaN(hours) || weight <= 0 || drinks < 0 || hours < 0) {
bacValueElement.textContent = "Invalid Input";
return;
}
var weightKg;
if (weightUnit === "lbs") {
weightKg = weight / 2.205;
} else {
weightKg = weight;
}
var gramsOfAlcoholPerDrink = 14; // Standard grams of alcohol in a US standard drink
var totalAlcoholGrams = drinks * gramsOfAlcoholPerDrink;
var r; // Widmark factor
if (gender === "male") {
r = 0.68;
} else {
r = 0.55;
}
// Calculate initial peak BAC using Widmark formula: (A / (W * r)) * 100
var initialBAC = (totalAlcoholGrams / (weightKg * r)) * 100;
// Calculate alcohol metabolized over time
var metabolismRatePerHour = 0.015; // Average BAC drop per hour
var alcoholMetabolized = hours * metabolismRatePerHour;
// Calculate final estimated BAC
var estimatedBAC = initialBAC – alcoholMetabolized;
// Ensure BAC doesn't go below zero
if (estimatedBAC < 0) {
estimatedBAC = 0;
}
// Display the result, formatted to 3 decimal places
bacValueElement.textContent = estimatedBAC.toFixed(3) + "%";
}