(e.g., 12oz beer, 5oz wine, 1.5oz spirits each count as 1 standard drink)
Your Estimated BAC: —
Status: Please enter values and click 'Calculate'.
function calculateBAC() {
var numDrinks = parseFloat(document.getElementById('numDrinks').value);
var weightLbs = parseFloat(document.getElementById('weightLbs').value);
var genderMale = document.getElementById('genderMale').checked;
var hoursSinceDrink = parseFloat(document.getElementById('hoursSinceDrink').value);
var bacResultDiv = document.getElementById('bacResult');
var bacStatusDiv = document.getElementById('bacStatus');
if (isNaN(numDrinks) || numDrinks < 0 || isNaN(weightLbs) || weightLbs <= 0 || isNaN(hoursSinceDrink) || hoursSinceDrink < 0) {
bacResultDiv.innerHTML = 'Your Estimated BAC: –';
bacStatusDiv.innerHTML = 'Status: Please enter valid positive numbers for all fields.';
bacStatusDiv.style.backgroundColor = '#f8d7da';
bacStatusDiv.style.borderColor = '#f5c6cb';
bacStatusDiv.style.color = '#721c24';
return;
}
// Widmark Formula Constants
var alcoholGramsPerStandardDrink = 14; // Approximately 14 grams of pure alcohol per standard drink in the US
var distributionRatioR; // r value (body water content)
var metabolismRate = 0.015; // BAC reduction per hour
if (genderMale) {
distributionRatioR = 0.68; // For men
} else {
distributionRatioR = 0.55; // For women
}
// Convert weight from lbs to grams (1 lb = 453.592 grams)
var bodyWeightGrams = weightLbs * 453.592;
// Total alcohol consumed in grams
var totalAlcoholGrams = numDrinks * alcoholGramsPerStandardDrink;
// Calculate initial BAC using Widmark formula
// BAC = (Alcohol in grams / (Body weight in grams * r)) * 100
var initialBAC = (totalAlcoholGrams / (bodyWeightGrams * distributionRatioR)) * 100;
// Account for alcohol metabolized over time
var metabolizedBAC = hoursSinceDrink * metabolismRate;
var finalBAC = initialBAC – metabolizedBAC;
// Ensure BAC doesn't go below zero
if (finalBAC < 0) {
finalBAC = 0;
}
var bacPercentage = finalBAC.toFixed(3);
bacResultDiv.innerHTML = 'Your Estimated BAC: ' + bacPercentage + '%';
var statusMessage = ";
var statusBgColor = ";
var statusBorderColor = ";
var statusTextColor = ";
if (finalBAC >= 0.25) {
statusMessage = 'Status: Severe Impairment – Risk of alcohol poisoning, loss of consciousness.';
statusBgColor = '#f8d7da'; // Reddish
statusBorderColor = '#f5c6cb';
statusTextColor = '#721c24';
} else if (finalBAC >= 0.15) {
statusMessage = 'Status: Major Impairment – Significant loss of balance, coordination, and judgment.';
statusBgColor = '#f8d7da'; // Reddish
statusBorderColor = '#f5c6cb';
statusTextColor = '#721c24';
} else if (finalBAC >= 0.08) {
statusMessage = 'Status: Legally Impaired – Driving is illegal and dangerous. Significant impairment of motor skills and judgment.';
statusBgColor = '#f8d7da'; // Reddish
statusBorderColor = '#f5c6cb';
statusTextColor = '#721c24';
} else if (finalBAC >= 0.05) {
statusMessage = 'Status: Impaired – Reduced coordination, altered judgment, difficulty tracking moving objects.';
statusBgColor = '#fff3cd'; // Yellowish
statusBorderColor = '#ffeeba';
statusTextColor = '#856404';
} else if (finalBAC > 0) {
statusMessage = 'Status: Slight Impairment – Mild euphoria, relaxation, slight decrease in reaction time.';
statusBgColor = '#d4edda'; // Greenish
statusBorderColor = '#c3e6cb';
statusTextColor = '#155724';
} else {
statusMessage = 'Status: Sober – No alcohol detected or fully metabolized.';
statusBgColor = '#d4edda'; // Greenish
statusBorderColor = '#c3e6cb';
statusTextColor = '#155724';
}
bacStatusDiv.innerHTML = statusMessage;
bacStatusDiv.style.backgroundColor = statusBgColor;
bacStatusDiv.style.borderColor = statusBorderColor;
bacStatusDiv.style.color = statusTextColor;
}
Understanding Blood Alcohol Content (BAC)
Blood Alcohol Content (BAC) is a measure of the amount of alcohol in your blood, expressed as a percentage. For example, a BAC of 0.10% means that there are 0.10 grams of alcohol for every 100 milliliters of blood.
How BAC is Calculated (The Widmark Formula)
This calculator uses a simplified version of the Widmark formula, a widely accepted method for estimating BAC. The core idea is to determine the total amount of alcohol consumed and distribute it across the body's water content. Key factors include:
Number of Standard Drinks: A standard drink typically contains about 14 grams of pure alcohol (e.g., 12 oz beer, 5 oz wine, 1.5 oz spirits).
Body Weight: Heavier individuals generally have more body water, which dilutes the alcohol more effectively.
Biological Sex: Women typically have less body water and higher body fat percentages than men, leading to a higher BAC for the same amount of alcohol consumed. This is represented by the 'r' (distribution ratio) value in the formula (approx. 0.68 for men, 0.55 for women).
Time Elapsed: The liver metabolizes alcohol at a relatively constant rate, typically around 0.015% BAC per hour. This calculator subtracts the metabolized alcohol over the specified time.
Factors Affecting BAC (Beyond the Calculator)
While this calculator provides an estimate, many other factors can influence your actual BAC:
Food Consumption: Eating before or while drinking slows the absorption of alcohol into the bloodstream.
Type of Drink: Carbonated drinks can speed up alcohol absorption.
Medications: Certain medications can interact with alcohol, affecting its absorption and metabolism.
Fatigue and Stress: These can influence how your body processes alcohol.
Individual Metabolism: Everyone metabolizes alcohol at a slightly different rate.
Hydration Level: Dehydration can lead to higher BAC levels.
Legal Limits and Impairment
In most parts of the United States, the legal limit for driving is a BAC of 0.08%. However, impairment can begin at much lower levels. Even a BAC of 0.02% can affect judgment and reaction time. It is always safest to avoid driving after consuming any alcohol.
Disclaimer: This Blood Alcohol Content (BAC) calculator is for informational and educational purposes only. It provides an estimate based on common formulas and averages. Actual BAC levels can vary significantly due to individual physiological differences, health conditions, and other factors. Do not use this calculator to determine if you are fit to drive or operate machinery. Always err on the side of caution. If you have consumed alcohol, do not drive. Arrange for a designated driver, use public transportation, or call a taxi/rideshare service.