Alcohol Blood Calculator

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Blood Alcohol Content (BAC) Calculator

Male Female
Estimated Blood Alcohol Concentration: 0.00%

Note: This is an estimate only. Never drink and drive.

How Blood Alcohol Content is Calculated

Blood Alcohol Content (BAC) represents the percentage of alcohol present in your bloodstream. This calculator uses the Widmark Formula, the industry standard for estimating alcohol distribution in the body. The formula takes into account your weight, gender (due to average body water content differences), the amount of alcohol consumed, and the rate of metabolism over time.

Disclaimer: This tool provides a mathematical estimate based on averages. Individual results vary significantly based on metabolism, recent food intake, hydration, and medication. This should never be used to determine if it is "safe" to drive.

The Widmark Formula Explained

The calculation follows this logic:

  • Alcohol in Grams: The volume of the drink (ml) multiplied by the alcohol percentage (ABV) and the density of ethanol (approximately 0.8).
  • Distribution Ratio: Men generally have a higher percentage of water (approx 0.68), while women have a lower distribution ratio (approx 0.55).
  • Metabolism: The human body typically metabolizes alcohol at a rate of roughly 0.015% BAC per hour.

BAC Levels and Effects

Understanding what these numbers mean is crucial for safety:

  • 0.02% – 0.03%: Feeling of relaxation, slight warmth. Minimal impairment.
  • 0.05% – 0.08%: Impaired judgment, lowered inhibitions, slowed physical reactions. In many regions, 0.08% is the legal driving limit.
  • 0.10% – 0.15%: Significant motor impairment, slurred speech, loss of balance.
  • 0.20%+: Severe intoxication, potential blackouts, risk of alcohol poisoning.

Example Calculation

If a 80kg male consumes three 355ml beers at 5% ABV over a period of 2 hours:

  1. Total alcohol consumed: ~42.6 grams.
  2. Widmark factor for male: 0.68.
  3. Initial BAC before metabolism: ~0.078%.
  4. After 2 hours of metabolism (0.015 x 2): Estimated BAC = 0.048%.
function calculateBAC() { var gender = document.getElementById("bac_gender").value; var weight = parseFloat(document.getElementById("bac_weight").value); var drinks = parseFloat(document.getElementById("bac_drinks").value); var abv = parseFloat(document.getElementById("bac_abv").value); var volume = parseFloat(document.getElementById("bac_volume").value); var time = parseFloat(document.getElementById("bac_time").value); var resultBox = document.getElementById("bac_result_box"); var display = document.getElementById("bac_display"); var status = document.getElementById("bac_status"); if (isNaN(weight) || isNaN(drinks) || isNaN(abv) || isNaN(volume) || isNaN(time) || weight <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Widmark Factor (r) var r = (gender === "male") ? 0.68 : 0.55; // Convert weight to grams var weightInGrams = weight * 1000; // Calculate total alcohol in grams // (Volume in ml * (ABV/100) * 0.8 density of ethanol) * number of drinks var alcoholGrams = (volume * (abv / 100) * 0.8) * drinks; // Calculate raw BAC // BAC = [Alcohol (g) / (Body Weight (g) * r)] * 100 var rawBac = (alcoholGrams / (weightInGrams * r)) * 100; // Subtract metabolism (Average 0.015% per hour) var metabolism = time * 0.015; var finalBac = rawBac – metabolism; if (finalBac < 0) { finalBac = 0; } // Display resultBox.style.display = "block"; display.innerText = finalBac.toFixed(3) + "%"; // Status Styling if (finalBac === 0) { status.innerText = "Sober"; status.style.backgroundColor = "#e8f5e9"; status.style.color = "#2e7d32"; } else if (finalBac < 0.05) { status.innerText = "Light Influence"; status.style.backgroundColor = "#fff3e0"; status.style.color = "#ef6c00"; } else if (finalBac < 0.08) { status.innerText = "Impaired – Caution"; status.style.backgroundColor = "#fffde7"; status.style.color = "#fbc02d"; } else { status.innerText = "Legally Intoxicated (in many areas)"; status.style.backgroundColor = "#ffebee"; status.style.color = "#c62828"; } // Smooth scroll to result resultBox.scrollIntoView({ behavior: 'smooth', block: 'nearest' }); }

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