BAC Calculator — Widmark Formula & Impairment Guide

The Formula

The Widmark formula estimates blood alcohol concentration based on the amount of alcohol consumed, body weight, sex (affecting alcohol distribution), and time elapsed. The elimination rate (0.015 g/dL per hour) is an average — actual rates vary from 0.010–0.025 based on genetics, liver function, food intake, and tolerance.

Variable Definitions

How to Use This Calculator

1. 1

   Enter your sex and body weight in pounds.

2. 2

   Enter the number of standard drinks consumed (12 oz beer / 5 oz wine / 1.5 oz liquor = 1 drink each).

3. 3

   Optionally enter the ABV if your drink differs from standard strengths.

4. 4

   Enter the number of hours since you started drinking.

5. 5

   Review the estimated BAC and the bold safety disclaimer. Never drive based on this estimate.

Common Applications

• Personal safety planning — estimate BACThe percentage of alcohol in your bloodstream. Used to measure intoxication levels and legal driving limits. and time until sober after drinking to make informed decisions about driving and other activities
• Legal awareness — understand how BACThe percentage of alcohol in your bloodstream. Used to measure intoxication levels and legal driving limits. relates to legal driving limits (0.08% in most US states) and the impairment levels that appear at different concentrations
• Educational demonstrations — the Widmark formula illustrates how body weight, sex, number of drinks, and elapsed time interact to affect blood alcohol concentration
• Social event planning — estimate the effects of different drinking patterns to plan safer consumption and understand why the same number of drinks affects people differently

Widmark formula estimates BAC from drinks consumed, body weight, sex, and elapsed time

Understanding the Concept

Blood Alcohol Concentration (BACThe percentage of alcohol in your bloodstream. Used to measure intoxication levels and legal driving limits.) measures the amount of alcohol in your bloodstream. The Widmark formula has been used since 1932 and remains the standard for forensic BACThe percentage of alcohol in your bloodstream. Used to measure intoxication levels and legal driving limits. estimation. Alcohol is absorbed through the stomach and small intestine into the bloodstream, then metabolized primarily by the liver at a rate of approximately 0.015 g/dL per hour (about 1 standard drink per hour). Factors affecting actual BACThe percentage of alcohol in your bloodstream. Used to measure intoxication levels and legal driving limits. include: food intake (slows absorption), body composition (muscle holds more water than fat), liver health, genetics, medications, and tolerance. The same number of drinks produces different BACs at different times due to these factors. For example, a 200 lb man and a 130 lb woman who both consume 3 standard drinks over 2 hours will have very different estimated BACs — the man at approximately 0.055% and the woman at approximately 0.079%, which is just under the legal limit for him but over for her. This illustrates why body weight and sex are critical variables, not mere formality. Food in the stomach can reduce peak BACThe percentage of alcohol in your bloodstream. Used to measure intoxication levels and legal driving limits. by 50–60% compared to drinking on an empty stomach — a full meal before drinking significantly changes the outcome. However, once alcohol is absorbed, nothing speeds up elimination except time: coffee, cold showers, exercise, and vomiting do not lower BACThe percentage of alcohol in your bloodstream. Used to measure intoxication levels and legal driving limits.. This tool provides an estimate and is not legally or medically definitive. Never drive after consuming any alcohol.

Frequently Asked Questions

Sources & References