DISCLAIMER: This calculator provides a rough estimate based on the Widmark formula. Individual metabolism, food intake, and health conditions can significantly alter actual BAC levels. Never drink and drive.
How Blood Alcohol Content is Calculated
Blood Alcohol Content (BAC) measures the mass of alcohol per unit volume of blood. This calculator utilizes the Widmark Formula, the gold standard for forensic alcohol estimation. The formula considers your body weight, the amount of alcohol consumed, your biological sex (which affects water distribution in the body), and the rate at which your liver metabolizes alcohol over time.
What Counts as a "Standard Drink"?
For the most accurate calculation, it is vital to understand what constitutes a single drink. In the United States, one "standard" drink contains roughly 14 grams of pure alcohol, which is typically found in:
12 oz of Regular Beer: (approx. 5% alcohol)
5 oz of Wine: (approx. 12% alcohol)
1.5 oz of Distilled Spirits: (80 proof, approx. 40% alcohol)
BAC Levels and Their Effects
Alcohol affects every individual differently, but general impairment levels follow these patterns:
0.02% – 0.04%: Lightheadedness, relaxation, and minor impairment of judgment.
0.05% – 0.07%: Euphoria, lowered inhibitions, and slowed exaggerated reflexes.
0.08%: The legal driving limit in most US states. Significant impairment of motor coordination and balance.
0.10% – 0.12%: Clear deterioration of reaction time and control. Slurred speech.
0.15%+: Severe intoxication, vomiting, and major loss of balance.
Factors That Influence BAC
While this calculator provides a mathematical average, several variables can change the outcome:
Rate of Consumption: Drinking several drinks in one hour will spike BAC faster than drinking them over four hours.
Food Intake: Having food in the stomach slows the absorption of alcohol into the bloodstream.
Body Composition: Muscle tissue contains more water than fat tissue, which helps dilute alcohol more effectively.
Medication: Certain medications can interact with alcohol, increasing its effects or slowing metabolism.
function calculateBAC() {
var genderConstant = parseFloat(document.getElementById('gender').value);
var weightLbs = parseFloat(document.getElementById('weight').value);
var drinks = parseFloat(document.getElementById('drinks').value);
var hours = parseFloat(document.getElementById('hours').value);
var resultArea = document.getElementById('bac-result-area');
var bacOutput = document.getElementById('bac-output');
var legalWarning = document.getElementById('legal-warning');
if (isNaN(weightLbs) || isNaN(drinks) || isNaN(hours) || weightLbs <= 0) {
alert("Please enter valid numbers for all fields.");
return;
}
// Standard drink = 14 grams of alcohol
var alcoholGrams = drinks * 14;
// Convert lbs to grams (1 lb = 453.592 grams)
var weightGrams = weightLbs * 453.592;
// Widmark Formula: BAC = [Alcohol consumed in grams / (Body weight in grams * r)] * 100
var rawBAC = (alcoholGrams / (weightGrams * genderConstant)) * 100;
// Metabolism: Average rate is 0.015% per hour
var metabolismReduction = hours * 0.015;
var finalBAC = rawBAC – metabolismReduction;
// BAC cannot be negative
if (finalBAC = 0.08) {
bacOutput.style.color = "#e74c3c";
legalWarning.innerHTML = "Warning: You are likely above the legal driving limit (0.08%). Do not drive.";
} else if (finalBAC > 0 && finalBAC < 0.08) {
bacOutput.style.color = "#f39c12";
legalWarning.innerHTML = "Caution: You have alcohol in your system. Impairment begins below the legal limit.";
} else {
bacOutput.style.color = "#27ae60";
legalWarning.innerHTML = "Your BAC is at or near zero.";
}
// Smooth scroll to result
resultArea.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}