BAC Calculator — Blood Alcohol Content Estimator
Estimate blood alcohol content using the classic Widmark formula, based on sex, body weight, number of standard drinks, and hours elapsed. A rough educational estimate only — see the disclaimer below.
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1 standard drink = 14g pure alcohol (US definition — other countries vary).
📊 Estimated BAC
Disclaimer: This calculator gives a rough educational estimate only, using the standard Widmark formula, and is not medical advice. Actual BAC varies by individual physiology, food intake, medication, drink strength, and other factors this formula cannot capture. This tool must never be used to decide whether it is safe or legal to drive, operate machinery, or perform any activity requiring sobriety — it is not a legal or safety determination of any kind. If you have been drinking, do not drive; arrange another way home. Consult a doctor for any alcohol-related health concern.
How the Widmark Formula Works
The Widmark formula is a long-standing method for approximating how much alcohol has entered someone's bloodstream, based on how much they drank, their body weight, their sex, and how much time has passed for their body to start metabolizing it. This tool implements the standard version of that formula purely as an educational reference — it does not replace an actual breath, blood, or urine alcohol test.
BAC% = ((Alcohol grams ÷ (Weight grams × r)) × 100) − (0.015 × Hours elapsed)
- Alcohol grams = number of standard drinks × 14g (the US standard drink definition)
- Weight grams = body weight in kg × 1000
- r = the Widmark distribution ratio — approximately 0.68 for men, 0.55 for women
- 0.015 = an average metabolism rate, representing roughly how much BAC% the body clears per hour
The result is clamped at a minimum of 0%, since BAC obviously cannot go negative once fully metabolized.
Worked Example
A male weighing 80 kg who had 3 standard drinks over the last 2 hours:
- Alcohol grams = 3 × 14 = 42g
- Weight grams = 80 × 1000 = 80,000g
- BAC before metabolism = (42 ÷ (80,000 × 0.68)) × 100 = (42 ÷ 54,400) × 100 = 0.0772%
- Metabolism adjustment = 0.015 × 2 hours = 0.03%
- Estimated BAC = 0.0772% − 0.03% ≈ 0.047%
A Note on "Standard Drinks"
This calculator uses the common US standard drink definition of 14 grams of pure alcohol — roughly a 12 oz beer, a 5 oz glass of wine, or a 1.5 oz shot of spirits. Other countries define a standard drink differently (the UK, for example, uses 8 grams), so if you're thinking in a different country's drink sizes, treat the resulting estimate as even less precise than usual.
Reference BAC Bands (Informational Only)
These bands are commonly cited general reference points describing typical effects at different BAC levels — they are not a driving-safety or legal verdict, and individual response to alcohol varies widely:
| Estimated BAC | General Reference Description |
|---|---|
| Below 0.02% | Minimal measurable effect for most people |
| 0.02% – 0.05% | Relaxation, mild euphoria, some lowered inhibition |
| 0.05% – 0.08% | Reduced coordination and judgment become more noticeable |
| 0.08% and above | Considered legally impaired to drive in most US states |