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Blood Alcohol Concentration (BAC) Calculator
Biological Sex
Male
Female
Body Weight (lbs)
Number of Standard Drinks
1 drink = 12oz beer (5%), 5oz wine (12%), or 1.5oz shot (40%)
Hours Since First Drink
Estimate BAC %
Estimated BAC Level:
0.000%
LEGAL DISCLAIMER: This calculator is for informational purposes only and provides a theoretical estimate. It does not provide medical or legal advice. Alcohol metabolism varies significantly based on age, metabolism, food intake, and health. Never drink and drive.
How Blood Alcohol Concentration (BAC) is Calculated
This calculator utilizes the Widmark Formula , the gold standard for forensic alcohol calculation. Blood Alcohol Concentration (BAC) represents the percentage of your blood volume that is comprised of alcohol.
The mathematical equation used is:
BAC = [ (Alcohol G consumed in grams / (Body Weight in grams * Gender Constant)) * 100 ] – (Time in hours * 0.015)
Key Variables in the Calculation
Gender Constant (r): Generally, men have a higher percentage of water in their bodies. The average constant is 0.68 for men and 0.55 for women.Alcohol Content: A "standard drink" in the US contains approximately 14 grams of pure ethanol.Metabolism Rate: On average, the human body metabolizes alcohol at a rate of 0.015% BAC per hour.
BAC Reference Chart
BAC Range
General Effects
0.02% – 0.04%
Lightheadedness, relaxation, minor mood shifts.
0.05% – 0.07%
Exaggerated behavior, lowered inhibitions, impaired judgment.
0.08% +
Legal intoxication limit in most US states. Significant impairment of motor skills and balance.
0.15% – 0.20%
Severe intoxication, risk of blackout, nausea, and vomiting.
Factors That Influence Your BAC
While formulas provide a baseline, several biological factors can shift your actual BAC level:
Food Intake: Drinking on an empty stomach allows alcohol to enter the bloodstream much faster.Rate of Consumption: Chugging drinks leads to a sharper spike in BAC compared to sipping over several hours.Medication: Many prescription and over-the-counter drugs can interact with alcohol, heightening its effects.Body Composition: Muscle tissue contains more water than fat tissue, which helps dilute alcohol more effectively.
function calculateBAC() {
var gender = document.getElementById("bac-gender").value;
var weightLbs = parseFloat(document.getElementById("bac-weight").value);
var drinks = parseFloat(document.getElementById("bac-drinks").value);
var hours = parseFloat(document.getElementById("bac-hours").value);
var resultArea = document.getElementById("bac-result-area");
var display = document.getElementById("bac-display");
var message = document.getElementById("bac-message");
// Validation
if (isNaN(weightLbs) || weightLbs <= 0 || isNaN(drinks) || drinks < 0 || isNaN(hours) || hours < 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// Widmark Formula constants
// r = distribution ratio (0.68 for men, 0.55 for women)
var r = (gender === "male") ? 0.68 : 0.55;
// Weight conversion: lbs to grams
var weightGrams = weightLbs * 453.592;
// Alcohol conversion: 1 standard drink = 14 grams of pure alcohol
var alcoholGrams = drinks * 14;
// Raw BAC before time degradation
var rawBAC = (alcoholGrams / (weightGrams * r)) * 100;
// Metabolism: Average body clears 0.015% per hour
var elimination = hours * 0.015;
var finalBAC = rawBAC – elimination;
// BAC cannot be negative
if (finalBAC 0 && finalBAC = 0.05 && finalBAC < 0.08) {
message.innerText = "Significant Impairment – High Risk";
message.style.color = "#f57c00";
} else {
message.innerText = "Legally Intoxicated (DUI Level) – Danger";
message.style.color = "#d32f2f";
}
}