Note: This calculator is for informational purposes only. Many factors including metabolism, food intake, and medication can affect your actual BAC. Never drink and drive.
function calculateBAC() {
var genderConstant = parseFloat(document.getElementById('bac_gender').value);
var weightLbs = parseFloat(document.getElementById('bac_weight').value);
var numDrinks = parseFloat(document.getElementById('bac_drinks').value);
var hours = parseFloat(document.getElementById('bac_hours').value);
var resultArea = document.getElementById('bac-result-area');
var displayValue = document.getElementById('bac_value_display');
var displayMessage = document.getElementById('bac_message');
if (!weightLbs || weightLbs <= 0 || isNaN(numDrinks) || isNaN(hours)) {
alert("Please enter valid numbers for weight, drinks, and time.");
return;
}
// Widmark Formula
// BAC = [ (Alcohol in grams) / (Body weight in grams * r) ] * 100 – (Time in hours * β)
// One standard drink is ~14 grams of pure alcohol
var alcoholGrams = numDrinks * 14;
var weightGrams = weightLbs * 453.592;
var rawBAC = (alcoholGrams / (weightGrams * genderConstant)) * 100;
var metabolism = hours * 0.015; // Average metabolism rate is 0.015% per hour
var finalBAC = rawBAC – metabolism;
if (finalBAC = 0.08) {
resultArea.classList.add("bac-warning");
displayMessage.innerHTML = "Legally Intoxicated: You are at or above the legal driving limit in most jurisdictions. Do not drive.";
} else if (finalBAC >= 0.05) {
resultArea.classList.add("bac-legal");
displayMessage.innerHTML = "Impaired: Your cognitive and motor skills are significantly affected. It is unsafe to drive.";
} else if (finalBAC > 0) {
resultArea.classList.add("bac-safe");
displayMessage.innerHTML = "Some Impairment: You have alcohol in your system. Exercise caution.";
} else {
resultArea.classList.add("bac-safe");
displayMessage.innerHTML = "Sober: Your BAC is estimated at zero.";
}
}
Understanding Blood Alcohol Content (BAC)
Blood Alcohol Content, or BAC, is a measurement of the percentage of alcohol present in a person's bloodstream. It is the metric used by law enforcement and medical professionals to determine the level of intoxication. A BAC of 0.08% means that there are 0.08 grams of alcohol for every 100 milliliters of blood.
How the Widmark Formula Works
This calculator utilizes the Widmark Formula, the gold standard in forensic toxicology for estimating alcohol levels. The calculation takes into account several critical variables:
Body Weight: Alcohol is distributed throughout the water in your body. People with higher body mass generally have more water, which dilutes the alcohol more effectively.
Biological Sex: Men and women metabolize alcohol differently. On average, women have a lower percentage of body water and lower levels of the enzyme alcohol dehydrogenase, leading to higher BAC levels for the same amount of consumption.
Alcohol Quantity: We define a "standard drink" as roughly 14 grams of pure ethanol. This is equivalent to 12 ounces of regular beer (5% ABV), 5 ounces of wine (12% ABV), or 1.5 ounces of distilled spirits (40% ABV).
Elapsed Time: The human body metabolizes alcohol at a relatively constant rate, typically lowering BAC by about 0.015% per hour.
BAC Thresholds and Effects
Different levels of alcohol in the system produce varying physical and mental effects:
0.02% – 0.03%: Slight relaxation, slight warmth, and mood elevation.
0.05% – 0.06%: Noticeable impairment in coordination, lowered inhibitions, and slowed reaction times.
0.08%: The legal limit for driving in most of the United States. Significant impairment of motor skills and judgment.
0.10% – 0.12%: Slurred speech, loss of balance, and significant lack of coordination.
0.20%+: Severe intoxication, potential for "blackouts," nausea, and loss of consciousness.
Factors That Influence Results
While this calculator provides a mathematical estimate, several real-world factors can drastically change your actual BAC:
Food Consumption: Drinking on an empty stomach allows alcohol to be absorbed into the bloodstream much faster.
Metabolic Rate: Genetics and liver health play a massive role in how quickly your body clears alcohol.
Hydration: Dehydration can lead to a higher concentration of alcohol in the blood.
Medications: Many prescription and over-the-counter drugs can interact with alcohol, intensifying its effects.
Safe Practices
The only truly safe BAC for driving is 0.00%. If you have been consuming alcohol, always choose a designated driver, use a rideshare service, or stay where you are until you are completely sober. Time is the only factor that will lower your BAC; coffee, cold showers, or exercise do not speed up the metabolic process of the liver.