Blood Alcohol Content Calculator
The Body Metabolizes Alcohol on Its Own Clock
Blood alcohol content depends on how much alcohol entered the bloodstream relative to body size, offset by the roughly steady rate at which the liver clears it — not on how a person feels. The Widmark formula, developed in the 1930s and still the basis for most BAC estimation tools, models exactly that trade-off between intake, body water distribution, and elapsed time.
The Formula
BAC = (Alcohol Consumed (g) ÷ (Body Weight (g) × r)) × 100 − (0.015 × Hours)
r (distribution ratio) = 0.68 for men, 0.55 for women
Standard drink = 14 g of alcohol
The distribution ratio r accounts for the fact that alcohol disperses through body water, and women have proportionally less body water than men at the same weight — which is why the same drink count produces a higher estimated BAC for a woman than a man of equal weight.
Worked Example
An 80 kg man who has had 3 standard drinks over 2 hours: alcohol consumed is 3 × 14 = 42 g. Applying the formula gives a BAC of approximately 0.047%.
General BAC Reference Ranges
| BAC | General effect |
|---|---|
| Below 0.03% | Minimal impairment |
| 0.03% – 0.08% | Impaired — do not drive |
| 0.08% – 0.15% | Legally intoxicated in most jurisdictions |
| 0.15% and above | Severely impaired |
How to Use This Calculator
- Choose Metric or Imperial units.
- Select your sex.
- Enter your body weight.
- Enter the number of standard drinks consumed.
- Enter the hours elapsed since you started drinking.
- Select Calculate to see your estimated BAC and status.
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If you're planning a night out, the Water Intake Calculator can help you plan hydration alongside alcohol consumption.