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BAC Calculator

Estimate your Blood Alcohol Concentration (BAC) and time until sobriety using the Widmark formula.

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%
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Volume per drink in milliliters

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About this Calculator

Estimate your Blood Alcohol Concentration (BAC) and time until sobriety using the Widmark formula.

Formula & Calculations

Formula

BAC = (grams_alcohol / (weight_grams × r)) - (β × hours) × 100 | r (male) = 0.68, r (female) = 0.55 | β (metabolism) = 0.015 g/dL/hr
Where:
  • BAC=Blood Alcohol Concentration as a percentage (g/dL)
  • r=Widmark distribution ratio (0.68 male, 0.55 female)
  • β=Average alcohol elimination rate (0.015 g/dL per hour)
  • grams_alcohol=Total grams of pure alcohol consumed (drinks × volume × ABV% × 0.789)
  • hours=Time elapsed since drinking began

Assumptions

  • The Widmark formula assumes average metabolism; individual rates vary based on genetics, food intake, and liver health.
  • One standard drink = 14 g of pure alcohol (US). Calculator allows custom drink size and ABV.
  • Metabolism rate of 0.015 g/dL per hour is an average; actual rates range from 0.010 to 0.025.

Calculation Examples

Example 1

Inputs:Male, 80 kg, 4 drinks (12 oz, 5% ABV), drinking over 2 hours
Result:BAC: ~0.038%, ~2.6 hours until sober (below 0.02%)

Grams alcohol = 4 × 355 × 0.05 × 0.789 ≈ 56.0 g. BAC = (56.0 / (80000 × 0.68)) × 100 - 0.015 × 2 ≈ 0.073%. For 80 kg male, 0.25 hr per standard drink to eliminate.

Example 2

Inputs:Female, 60 kg, 3 drinks (5 oz wine, 12% ABV), drinking over 3 hours
Result:BAC: ~0.042%, ~3.4 hours until sober (below 0.02%)

Grams alcohol = 3 × 148 × 0.12 × 0.789 ≈ 42.0 g. BAC = (42.0 / (60000 × 0.55)) × 100 - 0.015 × 3 ≈ 0.082%. Higher BAC due to lower body water and distribution ratio.

Frequently Asked Questions

How accurate is the Widmark formula?

The Widmark formula provides a reasonable estimate for average individuals but can vary by ±30% depending on food consumption, genetics, medication, and liver function. It should never be used to determine if you're safe to drive.

How long does it take for alcohol to leave your system?

On average, the body metabolizes one standard drink (14 g alcohol) per hour, reducing BAC by approximately 0.015 g/dL per hour. However, this rate varies individually. Drinking coffee, cold showers, or exercising does not speed up alcohol metabolism.

What BAC is considered legally impaired?

In most jurisdictions, 0.08% BAC is the legal limit for driving. However, impairment begins at much lower levels — reaction time and judgment are affected at BAC levels as low as 0.02%. This calculator is educational only and should not guide driving decisions.