BAC Calculator

About the BAC Calculator

A BAC calculator (Blood Alcohol Content calculator) estimates your current blood alcohol concentration based on the number of drinks consumed, your body weight, sex, and elapsed time since you started drinking. BAC is expressed as a percentage — 0.08% (0.08 grams of alcohol per 100 mL of blood) is the legal driving limit in the USA, UK, Canada, and Australia. Our free BAC calculator uses the Widmark formula, the most widely validated algorithm for estimating blood alcohol content, and accounts for the metabolic elimination of alcohol over time at approximately 0.015% per hour. Understanding your BAC estimate helps you make informed decisions about whether to drive, how long to wait before driving, and how alcohol affects your cognitive and motor function at different concentration levels. Important: this calculator provides an estimate only — actual BAC varies based on factors including liver health, medications, food intake, hydration, tolerance, and individual metabolic variation. Never rely on any calculator or app to determine if you are legally or safely fit to drive; if in doubt, do not drive.

How It Works

Widmark formula: BAC = (Alcohol consumed in grams / (Body weight in grams x Distribution ratio)) x 100, then subtract (0.015 x hours elapsed). Distribution ratio (r): 0.68 for men, 0.55 for women (reflecting women's typically higher body fat percentage, which alcohol does not distribute into). Alcohol content per drink: standard US drink = 14g pure alcohol = 12 oz regular beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%). Example: 70 kg male, 3 standard drinks over 2 hours. Alcohol consumed = 3 x 14g = 42g. BAC before metabolism = (42 / (70,000 x 0.68)) x 100 = (42/47,600) x 100 = 0.0882%. Subtract 2 hours of elimination: 0.0882 - (0.015 x 2) = 0.0582% BAC estimate. This is below the 0.08% legal limit but note the significant impairment that still exists below 0.08%.

Tips & Best Practices

• ✓Impairment begins well before 0.08% BAC: at 0.02%, reaction time is already slowed. At 0.05%, judgement, tracking, and concentration are measurably impaired. Many countries use 0.05% as the legal limit precisely because research shows meaningful impairment at this level.
• ✓The 0.015% per hour elimination rate is an average — individuals with higher liver enzyme activity may metabolise alcohol slightly faster; those with liver disease significantly slower. Nothing speeds up metabolism: coffee, cold water, food after drinking, and exercise do not help.
• ✓Food slows alcohol absorption: eating a meal high in protein and fat before or while drinking significantly reduces the peak BAC reached by slowing gastric emptying and alcohol absorption into the bloodstream.
• ✓Women reach higher BAC than men at the same consumption: less body water and lower alcohol dehydrogenase enzyme activity mean women absorb approximately 30% more alcohol per drink than men of equal weight.
• ✓Morning-after driving: if you consumed significant alcohol the night before, residual BAC may still be above legal limits the next morning. A person who stopped drinking at midnight with a BAC of 0.12% may still be at 0.08% or above at 6:00 AM (4 hours = 0.06% eliminated, leaving 0.06%).
• ✓Zero tolerance laws: in the USA, drivers under 21 face zero tolerance laws (typically 0.01-0.02% legal limit). Commercial drivers (CDL) have a legal limit of 0.04%.
• ✓Medications and alcohol: many common medications including antihistamines, sleep aids, anti-anxiety drugs, and certain antibiotics significantly amplify the effects of alcohol and may produce dangerous impairment at BAC levels that would otherwise be mild.
• ✓This calculator is for educational and awareness purposes only. Reliable BAC measurement requires a calibrated breathalyser or blood test. Never use any app or formula to decide whether to drive after drinking.

Who Uses This Calculator

Adults use the BAC calculator educationally to understand how the number of drinks they have consumed translates into concrete blood alcohol levels, making the abstract concept of "too drunk to drive" tangible and numerically grounded. Designated drivers and event hosts use it to help guests understand their level of impairment and plan transportation accordingly. Healthcare and public health educators use BAC calculations in alcohol awareness programmes, DUI prevention campaigns, and responsible service training. Medical students and pharmacology students use Widmark formula calculations to understand alcohol pharmacokinetics. Bartenders and servers use BAC awareness to support responsible service decisions. People calculating how many hours to wait before driving after social drinking use it to understand that "sleeping it off" may or may not be sufficient depending on the volume consumed.