BAC Calculator

What this calculator does

This calculator estimates your Blood Alcohol Concentration (BAC) based on the number of drinks consumed, your body weight, biological sex, and the time elapsed since you started drinking. BAC is expressed as a percentage representing grams of alcohol per 100 milliliters of blood.

Understanding BAC is important for personal safety, legal awareness, and responsible decision-making. In all US states, a BAC of 0.08% is the legal limit for driving (0.05% in Utah, and lower thresholds apply to commercial drivers and minors). However, impairment begins well before the legal limit—coordination, judgment, and reaction time are affected at BAC levels as low as 0.02–0.04%.

This tool is intended for educational purposes only. Individual alcohol metabolism varies significantly based on genetics, food intake, medications, hydration, fatigue, and other factors. Never rely solely on a BAC estimate to determine whether it is safe to drive.

How to use it

1. Enter the number of standard drinks consumed (one drink = 12 oz beer, 5 oz wine, or 1.5 oz spirits).
2. Enter your body weight in pounds (or kg).
3. Select your biological sex (affects the distribution ratio used in the formula).
4. Enter the time elapsed since your first drink (in hours).
5. Review your estimated BAC, time until sober, and impairment level.

Formulas used

• Widmark formula: BAC = (Alcohol consumed in grams / (Body weight in grams × r)) × 100 − (0.015 × Hours)

  Where:

  • Alcohol in grams = Number of drinks × 14 grams per standard drink
  • r = distribution ratio (0.73 for males, 0.66 for females)
  • 0.015 = average BAC reduction per hour (alcohol elimination rate)

• Simplified version: BAC ≈ (Drinks × 5.14 / (Weight in lbs × r)) − (0.015 × Hours)

• Time to sober (BAC = 0): Hours = Current BAC / 0.015

Examples

Example 1 — Social drinker: 3 beers over 2 hours. Male, 180 lbs. BAC = (3 × 5.14) / (180 × 0.73) − (0.015 × 2) = 0.117 − 0.030 = 0.087%. Above the legal limit.

Example 2 — Light drinking: 2 glasses of wine over 3 hours. Female, 140 lbs. BAC = (2 × 5.14) / (140 × 0.66) − (0.015 × 3) = 0.111 − 0.045 = 0.066%. Below 0.08% but impairment is still present.

Example 3 — Heavy consumption: 6 drinks over 3 hours. Male, 200 lbs. BAC = (6 × 5.14) / (200 × 0.73) − (0.015 × 3) = 0.211 − 0.045 = 0.166%. Severely impaired. Estimated time to sober ≈ 11 hours.

Tips and common mistakes

• This is an estimate, not a breathalyzer. Individual metabolism varies by 20–30%. Food in your stomach, hydration, medications, liver health, and tolerance all affect actual BAC. Never use this calculator to decide if you are safe to drive.
• A "standard drink" has a specific definition. 12 oz of 5% beer, 5 oz of 12% wine, or 1.5 oz of 40% spirits each contain about 14 grams of pure alcohol. Craft beers (7–12% ABV), large pours, and mixed drinks often contain 1.5–3 standard drinks.
• Your body eliminates alcohol at a fixed rate of roughly 0.015% BAC per hour (about one standard drink per hour). Coffee, water, food, and cold showers do not speed this up—only time does.
• BAC continues to rise for 30–60 minutes after your last drink as alcohol is absorbed from the stomach and intestines. Your peak BAC may be higher than your current estimate if you recently stopped drinking.
• Impairment starts below the legal limit. At 0.04% BAC, reaction time and coordination are already reduced. The safest choice is always a designated driver, rideshare, or no driving at all.
• Legal limits vary internationally. Many European and Asian countries set limits at 0.05% or 0.02%. Some countries (e.g. parts of India, Hungary) have a 0.00% limit.