Updated · Methodology: named formula library
BAC Calculator
Estimate your Blood Alcohol Content based on drinks consumed, weight, and time.
Widmark estimate: 3 drinks, 160 lbs, 2 hours = 0.055. US legal limit: 0.08.
Why This Calculation Matters
The BAC Calculator turns a well-known health formula into an instant lookup. It's most useful when you're tracking a number over time or comparing yourself against published reference ranges from bodies like the CDC, NIH, or WHO. Use it as one data point among many, not a diagnosis.
How to Use This Calculator
- Enter your values in the input fields, each one has a label and help text explaining what to type.
- Results appear instantly as you type; there's no "calculate" button to press.
- Change any input to compare scenarios side by side.
All math happens in your browser. Nothing you type is sent to a server, saved, or shared.
Reading Your Result
A single number tells you less than a trend. Track this value over weeks or months rather than obsessing over day-to-day variation. Hydration, sleep, and timing can all shift short-term readings without reflecting any real change.
Blood Alcohol Content
BAC is estimated using the Widmark formula which accounts for drinks consumed, body weight, gender, and time elapsed.
BAC Levels
- 0.02%: Light euphoria, relaxation
- 0.05%: Lowered inhibitions, mild impairment
- 0.08%: Legal limit for driving in most US states
- 0.10%: Clear impairment of motor control
- 0.15%: Major impairment, possible vomiting
- 0.30%+: Potential loss of consciousness, medical emergency
Important
This is an estimate only. Actual BAC varies based on food intake, hydration, medications, and individual metabolism. Never drive if you've been drinking.
Worked Example
3 standard drinks, 160 lb male, 2 hours
- drinks
- 3
- weight
- 160
- hours
- 2
- sex
- male
- Result
- BAC 0.055
(3 × 0.6 × 5.14)/(160 × 0.68) − 0.015 × 2 = 0.055. Below 0.08 legal limit.
When to Use This Calculator
- Track personal health metrics over time alongside guidance from your clinician.
- Understand how lifestyle changes may influence a given health number.
- Compare values against recognized reference ranges from CDC, NIH, or WHO.
Limitations & Common Mistakes
- Not a substitute for medical advice. Always consult a qualified clinician for anything that affects your care.
- Population-level formulas don't account for individual medical history, medications, or body composition nuances.
- Reference ranges evolve, use current CDC/NIH/WHO values when accuracy matters.
Frequently Asked Questions
What's Widmark's formula?
BAC = (drinks × 0.6 × 5.14) / (body weight in lbs × r) − 0.015 × hours since first drink. r is the distribution ratio: 0.68 for males, 0.55 for females. Standard drink = 14g pure alcohol (one 12oz beer at 5%, one 5oz wine at 12%, one 1.5oz spirit at 40%).
How accurate is the Widmark estimate?
Within ±0.02 BAC for most adults under typical conditions. Accuracy decreases with: empty stomach (BAC peaks higher), recent meal (BAC peaks lower and slower), unusual body composition, and individual variation in alcohol metabolism. Never use BAC estimates to decide whether to drive.
When is BAC at its peak?
30–90 minutes after the last drink, depending on stomach contents and alcohol type. Spirits peak fastest, beer slowest. The −0.015 × hours term in Widmark assumes you've already passed peak; for ongoing drinking, BAC is still rising.
What's the legal limit?
Driving: 0.08 in all U.S. states (0.05 in Utah). Commercial drivers: 0.04. Drivers under 21: typically 0.00–0.02 (zero-tolerance). Boating: 0.08 federal, varies by state. Even below 0.08, impairment begins around 0.02–0.04.
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Related guides
- TDEE: The Only Calorie Number That Actually Drives Weight ChangeBMR tells you the baseline. Calorie intake tells you the input. TDEE is the number that decides whether you lose, maintain, or gain, and it is the one most people miscalculate.
- BMI vs. Body Fat Percentage: Which Number Actually Measures HealthBMI is free and fast. Body fat percentage is more accurate. Waist-to-hip ratio predicts cardiovascular risk better than either. Here is when to use which, and what the CDC and WHO actually recommend.
Source: BLS Consumer Price Index, 2026.