Your estimated Blood Alcohol Content (BAC) will appear here.
Understanding Blood Alcohol Content (BAC) and Drink Driving Risks
The Alcohol Drink Drive Calculator estimates your Blood Alcohol Content (BAC) based on several factors. BAC is a measure of the amount of alcohol present in your bloodstream. Driving with a BAC above the legal limit is a serious offense and significantly impairs your ability to operate a vehicle safely.
How the Calculator Works: The Widmark Formula
This calculator uses a simplified version of the Widmark formula, a common method for estimating BAC. The formula considers your body weight, gender, the number of standard drinks consumed, and the time elapsed since drinking.
The general concept is:
BAC = (Alcohol consumed in grams) / (Body weight in grams * Distribution ratio) – (Alcohol metabolized per hour * Time elapsed)
Key Components:
Standard Drink: A standard drink contains approximately 10 grams of pure alcohol. The calculator assumes this standard.
Alcohol Consumption (grams): (Number of drinks * 10 grams/drink).
Body Weight: Your weight in kilograms is converted to grams (Weight in kg * 1000).
Distribution Ratio (r): This accounts for how alcohol distributes throughout the body's water content. It's generally higher for males (approx. 0.68) and lower for females (approx. 0.55) due to differences in body composition and water percentage.
Metabolism Rate: The body metabolizes alcohol at a relatively constant rate, typically around 0.015% BAC per hour. This means your BAC decreases over time as your body processes the alcohol.
Example Calculation:
Let's consider a 75 kg male who consumed 3 standard drinks over 2 hours.
This example shows how BAC changes over time. If the same person had drunk 3 drinks in a shorter period, their peak BAC would be higher.
Disclaimer:
This calculator provides an estimation only and should not be used as a definitive measure of legal sobriety. Many factors can influence BAC, including metabolism, food intake, hydration, and individual health conditions. Always err on the side of caution: if you have been drinking, do not drive. Arrange for a taxi, rideshare, or designated driver.
function calculateBAC() {
var weightKg = parseFloat(document.getElementById("weight").value);
var gender = document.getElementById("gender").value;
var drinks = parseFloat(document.getElementById("drinks").value);
var timeHours = parseFloat(document.getElementById("time").value);
var resultDiv = document.getElementById("result");
var warningDiv = document.getElementById("warningMessage");
resultDiv.style.display = 'block';
warningDiv.style.display = 'none';
resultDiv.innerHTML = 'Your estimated Blood Alcohol Content (BAC) will appear here.';
// Basic validation
if (isNaN(weightKg) || weightKg <= 0) {
resultDiv.innerHTML = "Please enter a valid weight.";
return;
}
if (isNaN(drinks) || drinks < 0) {
resultDiv.innerHTML = "Please enter a valid number of drinks.";
return;
}
if (isNaN(timeHours) || timeHours < 0) {
resultDiv.innerHTML = "Please enter a valid time.";
return;
}
var gramsPerDrink = 10; // Standard drink contains 10g of alcohol
var alcoholGrams = drinks * gramsPerDrink;
var weightGrams = weightKg * 1000; // Convert kg to grams
var distributionRatio;
if (gender === "male") {
distributionRatio = 0.68;
} else { // Female
distributionRatio = 0.55;
}
var bacEstimate = (alcoholGrams / (weightGrams * distributionRatio)); // BAC as a proportion
var metabolismRatePerHour = 0.015; // 0.015% per hour (or 0.00015 as a proportion)
var metabolizedAlcohol = metabolismRatePerHour * timeHours;
// Calculate final BAC (as a percentage)
var finalBAC = (bacEstimate – metabolizedAlcohol) * 100;
// Ensure BAC doesn't go below zero
if (finalBAC < 0) {
finalBAC = 0;
}
var bacPercentage = finalBAC.toFixed(3); // Display with 3 decimal places for precision
resultDiv.innerHTML = 'Estimated BAC: ' + bacPercentage + '%';
// Add warning messages based on BAC levels (example thresholds, may vary by region)
var warningText = "";
if (finalBAC > 0.05) { // Example threshold for exceeding common limits
warningText = "WARNING: Your estimated BAC is above the legal driving limit in many regions. DO NOT DRIVE.";
} else if (finalBAC > 0.02) {
warningText = "CAUTION: Even a low BAC can impair judgment and reaction time. Consider not driving.";
}
if (warningText) {
warningDiv.innerHTML = warningText;
warningDiv.style.display = 'block';
}
}