How to use Blood Alcohol Calculator
The blood alcohol calculator uses the Widmark formula to estimate blood alcohol concentration (BAC) from the number of drinks consumed, body weight, biological sex, and time elapsed since drinking began. The Widmark r-factor accounts for the different water content of male (0.68) and female (0.55) bodies. A standard drink elimination rate of 0.015% BAC per hour is applied. This tool is strictly for educational purposes — individual BAC varies significantly with food, medications, hydration and genetics, and the estimate must never be used to decide whether to drive.
- Select your biological sex (affects the Widmark distribution factor).
- Enter the number of standard drinks you consumed.
- Verify or adjust the grams of alcohol per drink (US = 14 g, UK = 8 g, EU = 10 g).
- Enter your body weight in kilograms.
- Enter the hours elapsed since your first drink.
- Click Estimate BAC and review the result alongside the effect reference table.
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The Widmark formula explained
The Widmark formula, developed by Swedish physician Erik Widmark in the 1930s, is: BAC = (A ÷ (W × r × 10)) − (β × t), where A = grams of alcohol consumed, W = body weight in kilograms, r = sex-specific distribution factor (0.68 male, 0.55 female), β = elimination rate (typically 0.015%/hour) and t = hours elapsed. The distribution factor r reflects the proportion of body water: males have more lean mass and hence more body water to dilute alcohol. The elimination step (β × t) models hepatic metabolism at a roughly constant rate.
BAC levels and typical effects
The effects of alcohol on cognition and coordination scale with BAC. Even at 0.02–0.05% — well below the legal limit in most jurisdictions — reaction time, divided attention and tracking performance are measurably impaired in controlled studies. The table below summarises typical effects, but individual variation (tolerance, fatigue, food intake, medications) can shift these ranges substantially.
| BAC (%) | Typical effects | Driving risk |
|---|---|---|
| 0.00–0.02 | Minimal to no perceptible effect | Baseline |
| 0.02–0.05 | Mild relaxation, slight euphoria, reduced inhibition | Measurably impaired |
| 0.05–0.08 | Reduced coordination, slower reaction time, impaired judgment | Clearly impaired |
| 0.08–0.15 | Clear impairment of coordination and cognition | Illegal in most countries |
| 0.15–0.30 | Severe impairment, possible nausea and disorientation | Extremely dangerous |
| 0.30+ | Life-threatening — risk of coma or respiratory arrest | Medical emergency |
Why this estimate can be inaccurate
The Widmark formula is a population-average model. Real BAC depends on stomach contents (food slows absorption by 50%), beverage type (carbonated drinks absorb faster), individual liver enzyme activity, concurrent medications, altitude, and body temperature. Peak BAC may also occur 30–90 minutes after drinking ends as absorption continues. A lower calculated BAC does not mean impairment is absent — and the estimate is never a safe basis for operating a vehicle.
Worked examples
Man, 2 drinks, 1 hour
Inputs: 80 kg male, 2 US drinks (28 g), 1 h
Result: ≈ 0.04% BAC (educational estimate — never drive)
Woman, 2 drinks, 1 hour
Inputs: 60 kg female, 2 US drinks (28 g), 1 h
Result: ≈ 0.07% BAC (educational estimate — never drive)
Glossary
- BAC
- Blood Alcohol Concentration — grams of alcohol per 100 mL of blood, expressed as a percentage.
- Widmark formula
- A pharmacokinetic model estimating BAC from alcohol consumed, body weight, sex, and time elapsed.
- Standard drink
- A unit of measurement for alcohol: 14 g pure ethanol in the US, 8 g in the UK, 10 g in the EU.
- Elimination rate (β)
- The rate at which BAC decreases per hour, approximately 0.015%/h on average.
- Distribution factor (r)
- The Widmark r-factor: 0.68 for males, 0.55 for females, reflecting body water content.
Related reading
Frequently Asked Questions
Why use Blood Alcohol Calculator?
- Applies the Widmark formula with sex-specific distribution factors for more physiologically accurate estimates
- Includes a configurable standard-drink size to match US, UK or EU alcohol unit definitions
- Shows BAC alongside a reference table of typical cognitive and coordination effects at each level
- Models alcohol elimination over time by subtracting the 0.015%/h metabolic clearance rate
Common use cases
- Understand how body weight affects BAC to illustrate why the same drink count affects people differently
- Estimate how many hours until BAC returns to zero after an evening of drinks as an educational exercise
- Compare male and female BAC estimates for the same intake to illustrate the Widmark r-factor difference
- Determine the approximate BAC after two standard drinks at dinner for general awareness purposes
- Use in a health or biology classroom to demonstrate pharmacokinetics and alcohol metabolism principles
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