Blood Alcohol Content Calculator

Calculate your estimated blood alcohol content (BAC) using the Widmark formula. Know when it's safe to drive.

Your Information

Enter your body weight

Standard drinks consumed

Each = 1 standard drink (14g alcohol)

Time elapsed since you started drinking

Enter your information and click Calculate to see your estimated blood alcohol content and when it's safe to drive.

Complete User Guide

What is Blood Alcohol Content (BAC)?

Blood Alcohol Content (BAC) is a measure of the amount of alcohol in your bloodstream, expressed as a percentage. It's used to determine legal intoxication levels and assess impairment.

BAC is measured in grams of alcohol per 100 milliliters of blood. For example, a BAC of 0.08% means 0.08 grams of alcohol per 100 milliliters of blood.

Legal BAC Limits

United States

Legal limit: 0.08% BAC for drivers 21 and over. Zero tolerance (0.00-0.02%) for drivers under 21.

Canada

Legal limit: 0.08% BAC (0.05% in some provinces). Zero tolerance for drivers under 21 or with learner's permits.

United Kingdom

Legal limit: 0.08% BAC in England, Wales, and Northern Ireland. 0.05% in Scotland.

BAC Effects by Level

0.00% - 0.02%: No Effects

No noticeable effects. Safe to drive (if legally allowed).

0.02% - 0.05%: Mild Effects

Slight relaxation, mild mood elevation. Judgment and coordination may be slightly impaired.

0.05% - 0.08%: Impaired

Reduced coordination, impaired judgment, decreased alertness. NOT safe to drive.

0.08% - 0.15%: Significantly Impaired

Poor muscle coordination, balance problems, significantly impaired judgment. Illegal to drive.

0.15%+: Severely Impaired

Severe motor impairment, loss of physical control, possible blackouts. Medical attention may be needed.

How to Use This Calculator

  1. Select your gender (affects alcohol metabolism)
  2. Choose weight unit (kg or lbs) and enter your weight
  3. Enter the number of standard drinks consumed
  4. Select the type of drink (beer, wine, or liquor)
  5. Enter hours since your first drink
  6. Click 'Calculate BAC' to see your results
  7. Review charts and wait time before driving

What is a Standard Drink?

A standard drink contains approximately 14 grams (0.6 ounces) of pure alcohol. Examples:

• Beer: 12 ounces (355 ml) of regular beer (5% ABV)
• Wine: 5 ounces (148 ml) of wine (12% ABV)
• Liquor: 1.5 ounces (44 ml) of distilled spirits (40% ABV)

Note: Actual alcohol content varies by brand and type. This calculator uses average values.

Widmark Formula

This calculator uses the Widmark formula to estimate BAC:

BAC = (Alcohol in grams / (Weight in kg × r)) - (β × Hours)

r: Distribution ratio (0.68 for men, 0.55 for women)

β: Elimination rate (0.15 g/L per hour average)

The formula accounts for alcohol absorption, distribution in the body, and elimination over time.

Understanding Your Results

BAC Percentage

Your estimated blood alcohol content. This is an estimate and may vary based on individual factors.

Time to Zero BAC

Estimated hours until your BAC reaches zero. Only time can lower BAC - coffee, food, or exercise do not speed up elimination.

Legal Limit Status

Indicates whether your BAC is above or below the legal driving limit (0.08% in most US states).

⚠️ Important Safety Warnings

  • This calculator provides ESTIMATES only. Actual BAC can vary significantly based on metabolism, food intake, medication, and other factors.
  • NEVER drink and drive. If you've consumed any alcohol, arrange for a designated driver, use public transportation, or call a taxi/ride-share service.
  • Only time can lower BAC. Coffee, cold showers, food, or exercise do NOT reduce BAC or make you sober.
  • Drinking and driving is illegal and dangerous. Penalties include fines, license suspension, and imprisonment. You could kill yourself or others.

Factors That Affect BAC

Body Weight: Heavier people generally have lower BAC for the same amount of alcohol.

Gender: Women typically have higher BAC than men for the same amount of alcohol due to body composition differences.

Food: Eating before or while drinking slows alcohol absorption.

Metabolism: Individual metabolic rates vary, affecting how quickly alcohol is processed.

Medications: Some medications can interact with alcohol and increase impairment.

Rate of Consumption: Drinking quickly increases BAC faster than drinking slowly.

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