The Blood Alcohol Content (BAC) calculator estimates the percentage of alcohol in your bloodstream based on several factors. It's crucial to understand that this is an estimation, and actual BAC can vary due to individual metabolism, food intake, and other physiological factors. This calculator is for informational purposes only and should not be used to determine one's fitness to drive or operate machinery. Always exercise caution and make responsible decisions regarding alcohol consumption.
How the BAC is Calculated
The formula used is a modified version of the Widmark formula, which is a common method for estimating BAC. The general principle involves calculating the amount of alcohol consumed, accounting for body weight and the distribution of alcohol in the body (which differs between genders), and then adjusting for the rate at which the body metabolizes alcohol over time.
The simplified calculation generally follows these steps:
Alcohol Weight Calculation: Determine the total weight of alcohol consumed. A standard drink is often considered to contain approximately 14 grams (0.6 ounces) of pure alcohol.
Body Water Percentage: Men generally have a higher percentage of body water than women, meaning alcohol distributes more widely in their bodies, resulting in a lower BAC for the same amount of alcohol consumed.
BAC Estimation Formula (Simplified):
For Males: BAC = (Amount of Alcohol in grams / (Body Weight in kg * 0.68)) * 100 - (Metabolism Rate * Hours)
For Females: BAC = (Amount of Alcohol in grams / (Body Weight in kg * 0.55)) * 100 - (Metabolism Rate * Hours)
Where:
Amount of Alcohol in grams = Number of standard drinks * 14 grams/drink
Body Weight in kg: Convert input weight to kilograms if necessary.
0.68 is the approximate volume of distribution for males.
0.55 is the approximate volume of distribution for females.
100 converts the ratio to a percentage.
Metabolism Rate is typically around 0.015% per hour, meaning the body eliminates about 0.015% BAC every hour.
Hours is the time elapsed since the first drink.
Result Formatting: The final result is displayed as a percentage (%).
Understanding Standard Drinks
A "standard drink" is a convenient way to measure alcohol content across different types of beverages. In most regions, a standard drink contains approximately 14 grams (or 0.6 fluid ounces) of pure alcohol. This typically corresponds to:
12 ounces (355 ml) of regular beer (about 5% alcohol)
5 ounces (148 ml) of wine (about 12% alcohol)
1.5 ounces (44 ml) of distilled spirits (like vodka, whiskey, gin – about 40% alcohol)
Note that actual alcohol content can vary, so it's essential to check labels if precision is important.
Factors Affecting BAC
Several factors can influence your BAC beyond the basic calculation:
Food Intake: Drinking on an empty stomach leads to faster alcohol absorption and higher BAC.
Body Composition: Muscle tissue holds more water than fat tissue, impacting alcohol distribution.
Medications: Certain medications can interact with alcohol and affect its metabolism.
Fatigue and Hydration: Dehydration and tiredness can sometimes make the effects of alcohol feel more pronounced.
Genetics and Liver Health: Individual differences in enzyme activity can affect how quickly alcohol is processed.
Disclaimer
This calculator provides an ESTIMATE of BAC. It is not a diagnostic tool and should not be used for legal or medical purposes. Laws regarding driving under the influence (DUI) vary significantly by jurisdiction, and even a low estimated BAC can impair judgment and reaction time. If you have consumed alcohol, do not drive. Arrange for a designated driver, taxi, or rideshare service.
function calculateBAC() {
var weight = parseFloat(document.getElementById("weight").value);
var weightUnit = document.getElementById("weightUnit").value;
var gender = document.getElementById("gender").value;
var drinks = parseFloat(document.getElementById("drinks").value);
var hours = parseFloat(document.getElementById("hours").value);
var resultElement = document.getElementById("result");
// Clear previous error messages or results
resultElement.innerHTML = '0.00% BAC';
// — Input Validation —
if (isNaN(weight) || weight <= 0) {
alert("Please enter a valid body weight.");
return;
}
if (isNaN(drinks) || drinks < 0) {
alert("Please enter a valid number of drinks.");
return;
}
if (isNaN(hours) || hours < 0) {
alert("Please enter a valid time in hours.");
return;
}
// — Calculations —
// Convert weight to kilograms if necessary
var weightKg = weight;
if (weightUnit === "lbs") {
weightKg = weight * 0.453592; // 1 lb = 0.453592 kg
}
// Amount of alcohol in grams (standard drink = 14g)
var alcoholGrams = drinks * 14;
// Alcohol distribution ratio (Widmark's constant)
var distributionRatio;
if (gender === "male") {
distributionRatio = 0.68; // Approx. 68% for males
} else { // female
distributionRatio = 0.55; // Approx. 55% for females
}
// Calculate BAC using a simplified Widmark formula
// BAC = (Alcohol Weight / (Body Weight * Distribution Ratio)) – (Metabolism Rate * Hours)
// Metabolism rate is approx 0.015% per hour
var bac = (alcoholGrams / (weightKg * distributionRatio)) – (0.015 * hours);
// Ensure BAC doesn't go below zero
if (bac < 0) {
bac = 0;
}
// Format the result to two decimal places
var formattedBAC = bac.toFixed(2);
// Display the result
resultElement.innerHTML = formattedBAC + '% BAC';
}