BAC Calculator
Estimate Blood Alcohol Content using the Widmark formula. For educational use only — never use this to decide whether to drive. Always plan a sober ride home.
How to Use
- Pick your sex (the body water distribution differs).
- Enter your weight in pounds.
- Enter the number of standard drinks consumed.
- Enter how many hours have elapsed since your first drink.
- Read the estimated BAC and how it compares to legal driving limits.
- This is an estimate only — DO NOT use to decide whether to drive.
Show Work
Notes
About the BAC Calculator
The BAC Calculator gives you a fast, free answer for health and fitness tracking without sending anything off your device. Estimate Blood Alcohol Content using the Widmark formula. For educational use only — never use this to decide whether to drive. Always plan a sober ride home.
How it works
Enter your figures and the result appears instantly, updating the moment you change anything. There is no submit button and nothing to wait for, so it is easy to try a few what-if numbers and compare the results. Just check each box holds the kind of value it expects.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
Is this legally accurate?
<strong>No.</strong> This is a rough estimate using the Widmark formula. Legal breathalyzer and blood tests are the only authoritative measurements. Many factors affect actual BAC that this calculator can't capture: food in stomach, hydration, medications, mucosal absorption rate, individual metabolism, and drinking pace. <strong>Never use this to decide whether to drive.</strong> Always plan a sober ride.
What's a 'standard drink'?
In the U.S.: 14 grams of pure alcohol — equivalent to 12 oz of regular beer (5% ABV), 5 oz of wine (12% ABV), or 1.5 oz of 80-proof spirits (40% ABV). Many craft beers, cocktails, and large pours contain multiple standard drinks. A 16 oz IPA at 8% ABV is about 2 standard drinks; a 'tall' margarita can be 2–3.
What are the U.S. legal limits?
<strong>0.08% BAC</strong> for drivers 21+ in 49 states. <strong>Utah is 0.05%</strong>. <strong>Commercial drivers (CDL):</strong> 0.04%. <strong>Under 21:</strong> 'zero tolerance' — typically 0.02% or any detectable amount, depending on state. Many countries are stricter: most of Europe is 0.05%, some Eastern European countries are 0.0%.
How fast does BAC drop?
About 0.015 BAC per hour for the average adult — alcohol metabolism is roughly linear once past the absorption phase. So a peak BAC of 0.10 takes about 6.5 hours to reach 0. There's nothing — coffee, cold showers, exercise, food — that significantly speeds metabolism. Only time.
Why are women affected more than men by the same drinks?
Women generally have higher percent body fat (lower percent body water) than men of the same weight, so the same amount of alcohol is distributed in less water and produces a higher BAC. Women also have less alcohol dehydrogenase (the stomach enzyme that pre-metabolizes alcohol). The Widmark formula uses different distribution constants (0.55 vs 0.68) to reflect this.
Does food really matter?
Yes. Eating before or while drinking slows alcohol absorption (the alcohol mixes with food and reaches the small intestine more gradually). Peak BAC on an empty stomach can be 50% higher than the same drinks with food. Once absorbed, food doesn't affect total alcohol — but it spreads the peak out over more time.
How do I use the BAC Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Does it cost anything or need an account?
No. The tool is completely free, there is no account to create, and it keeps working offline after the page first loads.
Is anything I type uploaded?
No. The tool works entirely on your device, so the values you enter never leave your browser.
Common Use Cases
Educational understanding
Learn how BAC scales with body weight, sex, and time — useful for designated-driver planning.
Planning a long event
Get a rough sense of how many drinks over what time span keeps a person under common impairment thresholds (still: don't drive).
Research and writing
Reference numbers when writing about drinking, dosing, or alcohol-related health topics.
Bartender training
Understand how alcohol affects different patrons differently to identify when to slow service.
Health curiosity
See how a 'standard' drink translates into BAC for your specific size — often surprising.
Recovery and sobriety
Understand how long alcohol persists in the body when planning travel or screenings (note: many tests detect alcohol metabolites for far longer than BAC remains positive).
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