BAC Calculator (Educational)
Estimate blood alcohol concentration using the Widmark formula. Strictly educational — never use BAC estimates to decide whether you're safe to drive.
Estimated BAC
⚠ Critical disclaimer
This calculator is for educational and informational purposes only.It is nota substitute for a breathalyzer or a way to confirm you're below the legal driving limit. Real BAC varies ±15–25% from formula estimates based on food, medications, hormones, individual physiology, and many factors this calculator can't model.
If you have been drinking, do not drive. Use a rideshare, taxi, designated driver, or stay where you are. The cost of a ride is always less than a DUI, a crash, or worse. No drink is worth that.
The Widmark formula
Erik Widmark's 1932 equation is still the basis for nearly every BAC calculator. It estimates blood alcohol concentration as:
BAC = (ethanol grams / (body weight in grams × r)) × 100
where r(the “Widmark factor”) approximates body water as a fraction of body mass: typically 0.68 for men and 0.55 for women, reflecting average body composition differences. Then we subtract metabolism: BAC drops by about 0.015 per hour of elapsed time.
The formula treats people as average. Real bodies vary — leaner people have higher r (more water), heavier-fat-mass people have lower r (less water for distribution). BMI and lean mass affect the result more than the formula assumes.
Standard drink sizes (US)
A “standard drink” in the US contains about 14 grams of pure ethanol. Approximations:
- Beer (5% ABV): 12 oz
- Light beer (4.2% ABV): 12 oz (slightly less ethanol)
- IPA (7% ABV): 8.6 oz, but typically poured at 12 oz = 1.4 standard drinks
- Wine (12% ABV): 5 oz
- Strong wine (14% ABV): 4.3 oz
- Distilled spirits (40% ABV / 80 proof): 1.5 oz (a standard shot)
Real-world drinks usually exceed the standard. A 20-oz craft IPA is ~2.3 standard drinks. A double pour at a bar is 3 oz of spirits = 2 standard drinks. A 9-oz wine pour is ~1.8 standard drinks.
US legal BAC limits
- 0.08% — DUI/DWI threshold for drivers 21+ in 49 states.
- 0.05% — Utah's limit since 2018.
- 0.04% — commercial drivers (CDL) federal limit.
- 0.01–0.02% — zero-tolerance limits for drivers under 21 (varies by state).
- 0.15% — “enhanced” or “aggravated” DUI in many states with bigger penalties.
- 0.20% — even more enhanced charges in some states.
Even below the legal limit, driving while impaired can result in a DUI charge if an officer documents impairment. There's no “safe” BAC for driving.
What affects real-world BAC vs. the formula
- Food in stomach — food slows absorption, lowering peak BAC. Empty stomach drinks hit harder and faster.
- Type of drink — carbonated drinks (champagne, soda mixers) absorb faster. Sweet drinks absorb slower (sugar slows gastric emptying).
- Hydration — dehydration concentrates blood, raising apparent BAC for the same alcohol load.
- Medications — many medications interact with alcohol metabolism. Read labels.
- Hormonal cycle — women may experience higher peak BAC during certain phases of the menstrual cycle.
- Genetics — alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) variations cause major differences in metabolism rate. ALDH2 deficiency (common in East Asian populations) causes flushing and higher peak BAC.
- Age — older adults often have lower body water, leading to higher BAC for the same drinks.
There's no way to sober up faster
The liver processes alcohol at a roughly fixed rate (0.015 BAC/hour). Things that don't lower BAC, despite popular belief:
- Coffee. Makes you alert but still impaired (“wide-awake drunk”).
- Cold showers. Wakes you up; doesn't change BAC.
- Eating after drinking. Doesn't reverse intoxication. (Eating before can lower the peak.)
- Throwing up. Removes some unabsorbed alcohol from the stomach but doesn't affect what's already in the bloodstream.
- Exercise. Doesn't speed metabolism meaningfully.
The only fix is time. If you need to drive in 4 hours and your estimated BAC is 0.08, you're not safe yet. Plan a ride home before you start drinking.
Resources
If you drink: use Uber, Lyft, taxi, designated driver, or stay overnight.
If someone you know is showing signs of alcohol poisoning(confusion, vomiting, seizures, slow breathing, low body temperature, unconsciousness): call 911. Do not assume they'll “sleep it off.”
If you're struggling with alcohol use: SAMHSA National Helpline 1-800-662-HELP (4357), free and confidential, 24/7. Find a support group at AA.org or smartrecovery.org.