🍺 Blood Alcohol Content (BAC) Estimator

Estimate your approximate Blood Alcohol Concentration (BAC) using the Widmark formula. Enter weight, gender, drinks or total alcohol consumed, and time since the first drink. This tool provides an estimate only — never rely on it to determine fitness to drive or operate machinery.

Important: This estimator uses population-level constants and assumptions (Widmark). It gives only an estimate. Legal limits vary by jurisdiction and individual alcohol metabolism varies widely. Do not rely on this tool to decide whether it's safe to drive.

Blood Alcohol Concentration (BAC): what it measures and why it matters

The Blood Alcohol Concentration (BAC) represents the mass of alcohol per unit volume of blood and is commonly expressed as a percentage — for example, 0.08% BAC means 0.08 grams of alcohol per 100 milliliters of blood. BAC is a widely used metric to determine impairment from alcohol: as BAC rises, coordination, judgment, reaction time, and driving ability decline.

How BAC is estimated (Widmark formula)

This estimator uses the Widmark approach, which approximates BAC as a function of total alcohol consumed, body weight, a gender-specific distribution factor (r), and an elimination rate over time. The simplified Widmark equation is:

BAC = (A / (r × weight_kg)) - (beta × hours)

Where:

  • A is the total alcohol in grams.
  • r is the alcohol distribution ratio (average: 0.68 for men, 0.55 for women, and ~0.62 for others).
  • beta is the elimination rate (commonly ~0.015 %BAC per hour).

How to estimate alcohol (grams)

You can either enter a total grams of alcohol or let the calculator compute it from the number of standard drinks, the drink size, and the ABV (alcohol by volume). The formula to convert drink volume and ABV to grams of ethanol is:

grams = volume_ml × (ABV / 100) × 0.789

where 0.789 g/ml is the density of ethanol.

Typical impairment levels

These are approximate ranges — individual sensitivity varies:

  • 0.02%–0.05%: Mild relaxation, slight impairment of judgment.
  • 0.05%–0.08%: Increased impairment of coordination and reduced ability to drive safely; many countries set 0.05% or 0.08% as legal driving limits.
  • 0.08%–0.15%: Significant impairment; high risk to drive; slurred speech, poor balance.
  • >0.20%: Severe impairment, potential loss of consciousness, and medical risk.

Limitations and variability

The Widmark model simplifies real physiology. Several factors can alter BAC: genetics, liver function, recent food intake, hydration, medications, drinking pattern (binge vs. slow consumption), and tolerance. Therefore BAC estimates are approximate and should be used for educational purposes only.

Legal limits and safety

Legal BAC limits for driving vary by country and sometimes by state/province. Common legal thresholds are 0.05% or 0.08% for general driving; some places have lower limits for novice drivers or commercial drivers. Always check local laws and never drive if impaired.

Practical example

Example: a 75 kg man consumes 3 × 330 ml beers at 5% ABV over 2 hours. Each beer contains: 330 × 0.05 × 0.789 ≈ 13.0 g ethanol. Total A ≈ 39 g. Using r=0.68 and beta=0.015: BAC ≈ (39 / (0.68 × 75)) - (0.015 × 2) ≈ 0.0097 - 0.03 ≈ 0.078% (approx). This shows how modest drinking can approach common legal limits.

Using BAC estimates responsibly

Use this estimator to understand relative risk and plan safer choices (e.g., time to sober up, choosing not to drive, calling a taxi). For medical emergencies (suspected alcohol poisoning) contact emergency services immediately.

Frequently Asked Questions (FAQs)

BAC (Blood Alcohol Concentration) is the amount of alcohol in a person's blood, usually expressed as a percentage (grams per 100 mL).
It provides an estimate based on the Widmark formula and common assumptions. Individual metabolism varies widely, so results are approximate and for educational use only.
The Widmark formula estimates BAC from total alcohol consumed, a distribution ratio (r), body weight, and an elimination rate over time.
On average, alcohol is metabolized at about 0.010–0.020% BAC per hour. Complete elimination depends on starting BAC; for example, at 0.08% and 0.015%/hr it takes ~5–6 hours to return to zero.
Food slows alcohol absorption, which can lower peak BAC but does not change the total alcohol absorbed. Eating before or during drinking often reduces peak impairment.
Yes. Women typically have a lower alcohol distribution ratio (r), leading to higher BAC than men after consuming the same amount of alcohol per kg body weight.
Professional breathalyzers and blood tests are more accurate than calculators. Home breathalyzers vary in quality. For legal or medical decisions, use certified testing methods.
Warning signs include confusion, vomiting, seizures, slow or irregular breathing, blue-tinged skin, hypothermia, or unconsciousness. Call emergency services immediately if suspected.
Tolerance affects perceived impairment, not BAC. Heavy drinkers may feel less impaired at a given BAC but are still at risk of harm and legal consequences.
No. Use this tool for educational purposes only. Legal limits vary and individual impairment differs. Never rely solely on an online estimator to decide to drive.