How to Calculate Blood Alcohol Content (BAC)

A BAC calculator estimates your blood alcohol level based on drinks consumed, body weight, sex, and time elapsed. It helps promote awareness of alcohol impairment.

The Formula

BAC = (Alcohol oz x 5.14 / Body Weight x Gender Factor) - (0.015 x Hours)

Where:

BACBlood Alcohol Content — Percentage of alcohol in bloodstream
AlcoholAlcohol Consumed — Total ounces of pure alcohol
BWBody Weight — Weight in pounds
HoursTime Elapsed — Hours since first drink consumed

Step-by-Step Example

Here's how to calculate blood alcohol content (bac) step by step:

  1. 1Calculate alcohol consumed: Convert drinks to ounces of pure alcohol (one standard drink = 0.6 oz).
  2. 2Apply Widmark formula: Multiply alcohol by 5.14, divide by weight times gender constant (0.73 male, 0.66 female).
  3. 3Subtract metabolism: Subtract 0.015 for each hour since your first drink.

Following these 3 steps gives you the final blood alcohol content (bac) value.

Skip the Math

A 180-pound male who has 3 beers over 2 hours: BAC = (1.8 x 5.14) / (180 x 0.73) - (0.015 x 2) = approximately 0.04%.

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Why You Need This Calculation

  • Estimating BAC helps you understand impairment levels and make responsible decisions about driving.

Common Mistakes

Underestimating drink sizes.

A standard drink is 12 oz beer, 5 oz wine, or 1.5 oz spirits.

Assuming food prevents intoxication.

Food slows absorption but does not prevent BAC from rising.

Relying on BAC calculators for legal decisions.

Calculators provide estimates only; impairment begins well below 0.08%.

Frequently Asked Questions