BAC Calculator
Free Bac Calculator for health & fitness. Enter your measurements for personalized results with clear explanations and reference ranges.
Formula
BAC = (Alcohol × 5.14 / Weight × r) - (0.015 × hours)
The Widmark formula estimates BAC from alcohol consumed, body weight, sex, and elapsed time. Metabolism reduces BAC by about 0.015% per hour.
Worked Examples
Example 1: Calculate BAC After Drinks
Problem:180 lb male, 3 beers over 2 hours.
Solution:Using Widmark formula:\nWeight: 180 lbs\nSex factor (r): 0.68 (male)\nAlcohol: 3 × 0.6 oz = 1.8 oz\nTime: 2 hours\n\nRaw BAC = (1.8 × 5.14) / (180 × 0.68)\n= 9.25 / 122.4 = 0.076%\n\nAfter metabolism (0.015%/hr × 2hr = 0.03%):\nBAC = 0.076% - 0.030% = 0.046%\n\nJust under legal limit but impaired.
Result:BAC: 0.046% (below 0.08% but impaired)
Example 2: Time to Sober Calculation
Problem:Current BAC is 0.12%. How long until sober?
Solution:Current BAC: 0.12%\nMetabolism rate: 0.015%/hour\n\nTime to reach 0.08%:\n(0.12 - 0.08) / 0.015 = 2.7 hours\n\nTime to reach 0.00%:\n0.12 / 0.015 = 8 hours\n\nDO NOT DRIVE for at least 8 hours.\nEven after 3 hours (at 0.075%), you're impaired.
Result:8 hours to sober, 2.7 hours to legal limit
Example 3: Compare Male vs Female
Problem:Same weight (150 lbs), same drinks (2 glasses wine). Compare BAC.
Solution:Alcohol: 2 × 0.6 oz = 1.2 oz\nWeight: 150 lbs\n\nMale (r = 0.68):\nBAC = (1.2 × 5.14) / (150 × 0.68)\n= 6.17 / 102 = 0.060%\n\nFemale (r = 0.55):\nBAC = (1.2 × 5.14) / (150 × 0.55)\n= 6.17 / 82.5 = 0.075%\n\nFemale BAC is 25% higher from same alcohol.
Result:Male: 0.060% vs Female: 0.075%
Frequently Asked Questions
What is BAC?
Blood Alcohol Concentration (BAC) is the percentage of alcohol in your bloodstream. 0.08% means 0.08 grams of alcohol per 100 mL of blood. This is the legal driving limit in most US states. Even lower BAC levels cause impairment.
How accurate are BAC calculators?
BAC calculators provide estimates only. Actual BAC depends on many factors: food in stomach, drinking speed, individual metabolism, medications, liver health, and genetics. Use calculators for general awareness, not to decide if you're safe to drive.
How does body weight affect BAC?
Heavier people have more body water to dilute alcohol, resulting in lower BAC from the same amount of alcohol. However, this doesn't mean heavier people are 'safer' drivers - impairment still occurs at the same BAC levels regardless of weight.
Why do women reach higher BAC than men?
Women typically have: less body water (alcohol dilutes more in water), more body fat (doesn't absorb alcohol), lower levels of alcohol dehydrogenase enzyme, and hormonal variations affecting metabolism. Same drinks result in higher BAC for women.