BAC Calculator
Estimate your blood alcohol content based on drinks, weight, gender, and time elapsed. For educational purposes only — never drink and drive.
Your Details
Estimated BAC
How BAC Is Calculated (Widmark Formula)
This calculator uses the Widmark Formula: BAC = (alcohol in grams) / (weight in kg × r × 10) − (0.015 × hours), where r = 0.68 for men and 0.55 for women (distribution factor reflecting body water content). Alcohol metabolizes at approximately 0.015% per hour on average.
Factors that increase BAC for the same drink amount: lower body weight, female sex (lower distribution factor), empty stomach, liver conditions, certain medications, lack of alcohol tolerance. This calculator uses population averages only.
Everything About the BAC Calculator
The formula, how it works, and essential safety tips for using BAC estimates responsibly.
How It Works
- Select biological sex (affects alcohol distribution ratio)
- Enter body weight in lbs or kg
- Add each drink with type and alcohol content
- Enter hours elapsed since drinking started
- See estimated BAC% and time until sober
The Formula
BAC = (A × 5.14 / W × r) − 0.015 × H
A = fluid oz of alcohol · W = body weight (lbs) · r = 0.73 (male) / 0.66 (female) · H = hours since first drink. Based on the Swedish pharmacologist Erik Widmark’s 1932 formula.
Pro Tips
- This is an estimate — individual metabolism varies ±30%. Never drive based on calculator output
- Food slows absorption by up to 50%; eating before drinking reduces peak BAC significantly
- Coffee, showers, and exercise do not lower BAC — only time does (~0.015%/hr)
- One standard drink = 14g pure alcohol = 12oz regular beer, 5oz wine, or 1.5oz spirits
Frequently Asked Questions
How is BAC calculated? +
The Widmark formula is most commonly used: BAC = (grams of alcohol) ÷ (body weight in grams × distribution ratio × 10) − (0.015 × hours since drinking). The distribution ratio is 0.68 for men and 0.55 for women, reflecting differences in body water percentage. Our calculator uses this formula and accounts for gender, body weight, and time elapsed since drinking.
How long until I'm completely sober? +
Approximately: BAC ÷ 0.015 = hours until BAC reaches zero. At 0.10% BAC, that's about 6.7 hours. At 0.15%, about 10 hours. This varies by individual — food slows absorption, and individual metabolism varies by genetics, liver health, and body composition. Nothing actually speeds up sobriety: not coffee, not cold showers, not exercise. Only time allows your liver to process the alcohol.
Can food or water lower my BAC? +
Food before or while drinking slows alcohol absorption into the bloodstream — it doesn't lower BAC already in your system. Water helps with hydration and hangover symptoms but doesn't speed up alcohol elimination. Coffee makes you feel more awake but doesn't reduce BAC — potentially creating a "wide awake drunk" who feels capable of driving but is still legally impaired.
What factors beyond drinks and weight affect BAC? +
Key factors include: gender (women absorb more alcohol due to lower body water percentage); food consumption (slows absorption); medications (many interact with alcohol); genetics (ADH enzyme variants affect metabolism speed); liver health; age (older adults metabolize alcohol more slowly); carbonation (sparkling mixers speed absorption). Tolerance changes your perception but not your BAC — a high-tolerance person can have a 0.12% BAC and feel fine, while being legally and physically impaired.
At what BAC does impairment begin? +
Measurable cognitive impairment begins around 0.02% BAC — well before the 0.08% legal limit. At 0.02–0.05%, reaction time slows slightly and multitasking becomes harder. At 0.05–0.08%, judgment, coordination, and tracking ability are noticeably reduced. The 0.08% legal limit does not mean driving is safe below that threshold — crash risk begins increasing at 0.02% and roughly doubles at 0.05%.