This calculator uses the Widmark Formula, the gold standard for estimating Blood Alcohol Concentration (BAC). BAC represents the percentage of your blood that is concentrated with alcohol. For example, a BAC of 0.08% means your blood contains 0.08 grams of alcohol for every 100 milliliters of blood.
The Widmark Formula
The math behind your level of intoxication is based on several biological variables:
Alcohol Consumed: We assume a standard drink contains roughly 14 grams of pure ethanol.
Body Weight: Alcohol distributes itself in the water content of the body. A larger person generally has more water, diluting the alcohol more effectively.
Gender Constant (r): Men generally have a higher water percentage (r = 0.68) than women (r = 0.55), who typically have a higher body fat percentage.
Metabolism: The liver processes alcohol at a relatively constant rate, typically lowering BAC by about 0.015% per hour.
What is a "Standard Drink"?
In the United States, a standard drink is defined as any beverage containing approximately 0.6 fluid ounces or 14 grams of pure alcohol. This is roughly equivalent to:
12 ounces of regular beer (about 5% alcohol).
5 ounces of wine (about 12% alcohol).
1.5 ounces of distilled spirits (about 40% alcohol or 80 proof).
Important Safety Disclaimer
NEVER drink and drive. This calculator provides a theoretical estimate for educational purposes only. Factors like metabolism, recent food intake, hydration, and medication can drastically alter your actual BAC. A digital calculator cannot replace a professional breathalyzer or blood test. If you have been drinking, please use a designated driver or ride-sharing service.
function calculateBAC() {
var genderConstant = parseFloat(document.getElementById('gender').value);
var weight = parseFloat(document.getElementById('weight').value);
var weightUnit = document.getElementById('weightUnit').value;
var drinks = parseFloat(document.getElementById('drinks').value);
var hours = parseFloat(document.getElementById('timeElapsed').value);
var resultDiv = document.getElementById('bacResult');
var valueDisplay = document.getElementById('bacValue');
var statusDisplay = document.getElementById('bacStatus');
var sobrietyDisplay = document.getElementById('sobrietyTime');
if (isNaN(weight) || isNaN(drinks) || isNaN(hours) || weight <= 0) {
alert("Please enter valid numbers for weight, drinks, and time.");
return;
}
// Convert weight to grams
var weightInGrams;
if (weightUnit === 'lbs') {
weightInGrams = weight * 453.592;
} else {
weightInGrams = weight * 1000;
}
// Standard drink = 14 grams of alcohol
var alcoholConsumedGrams = drinks * 14;
// Widmark Formula: BAC = [Alcohol consumed (g) / (Body weight (g) * r)] * 100
var rawBAC = (alcoholConsumedGrams / (weightInGrams * genderConstant)) * 100;
// Metabolism reduction: 0.015% per hour
var reduction = hours * 0.015;
var finalBAC = rawBAC – reduction;
if (finalBAC < 0) finalBAC = 0;
// Display results
resultDiv.style.display = 'block';
valueDisplay.innerText = finalBAC.toFixed(3) + "%";
// Determine status and colors
if (finalBAC === 0) {
resultDiv.style.backgroundColor = "#e8f5e9";
statusDisplay.innerText = "Sober";
statusDisplay.style.color = "#2e7d32";
sobrietyDisplay.innerHTML = "";
} else if (finalBAC < 0.05) {
resultDiv.style.backgroundColor = "#fff9c4";
statusDisplay.innerText = "Slight Impairment / Relaxed";
statusDisplay.style.color = "#f57f17";
} else if (finalBAC 0) {
var hoursToSober = finalBAC / 0.015;
sobrietyDisplay.innerHTML = "Estimated time until 0.00% BAC: " + hoursToSober.toFixed(1) + " hours";
}
}