Blood Alcohol Content (BAC) Calculator
Estimate blood alcohol content from your drinks, weight and time. For education only — never use it to decide whether to drive.
Example: with Standard drinks 3 · Body weight 170 lb · Hours since first drink 2 hrs → Estimated BAC: 0.050.
- vs 0.08 legal limitUnder 0.08
- Time until 0.08% (common limit)Already below 0.08%
- Time until sober (0.00)3.3 more hours
Computed by the calculator below using its default values. Change any input to see your own numbers.
⚠ This calculator gives a rough estimate only. It cannot tell you whether it is safe for you to drive. See the disclaimer below the results.
⚠ Not driving advice, ever. This is a rough estimate from average constants — your real BAC can be considerably higher or lower depending on food in your stomach, medications, hydration, sleep, genetics and how quickly you drank. It cannot tell you whether you are safe to drive or operate machinery. The only BAC that is safe for driving is 0.00%. If you have had any alcohol, arrange a sober ride, taxi, rideshare, or stay where you are — do not get behind the wheel and do not use this number to talk yourself into it.
Rideshare and designated-driver resources
Learn moreAn estimate, never a green light
This uses the Widmark formula to estimate BAC from alcohol consumed, body water and time. Real BAC varies with food, medications, health and individual metabolism, so the number can be off in either direction. Never use any calculator to decide whether to drive — if you’ve been drinking, don’t.
This tool cannot and does not tell you whether you are safe to drive. Impairment starts well below the legal limit, individual tolerance and metabolism vary enormously, and no formula can measure your actual reaction time or judgment in the moment. If you have consumed any alcohol, the only responsible choice is not to drive — call a rideshare, use a taxi, get a sober driver, or stay put.
How it’s calculated & sources
This is the Widmark formula: BAC% ≈ (alcohol consumed in grams ÷ (body weight in grams × r)) × 100 − (elimination rate × hours), where r is the sex-based distribution ratio (commonly cited as ≈0.68 for men and ≈0.55 for women in standard references, though individual values vary) and the elimination rate is taken as a commonly cited average of 0.015% per hour (real-world estimates range roughly 0.010–0.020%/hour depending on the person).
In Standard drinks mode, alcohol consumed is drinks × 14 g, using the common U.S. definition of one standard drink ≈ 14 g (≈0.6 fl oz) of pure alcohol. In Size + ABV% mode, alcohol consumed is calculated from your actual pour: fl oz × ABV% × number of drinks × 29.57 mL/oz × 0.789 g/mL (the density of ethanol), which lets you model a specific beer, wine or liquor serving instead of assuming a flat standard-drink size.
“Time until 0.08%” and “time until sober” both work backward from your estimated peak BAC using the same 0.015%/hour elimination rate: time = (current estimate − target) ÷ 0.015. If your current estimate is already at or below the target, the calculator says so instead of showing a negative time.
Benchmark: 0.08% is the legal driving limit in most U.S. states (0.05% in Utah); the reference table above shows other commonly cited limits. This is an estimate for education only, not a measurement of your actual BAC or your fitness to drive.
Results update as you type and are general estimates, not personalized medical, legal, or safety advice — and they are never a substitute for a breathalyzer, blood test, or your own judgment. Verify with a professional, and when in doubt, don’t drive.
Frequently asked questions
What is a standard drink?
In the U.S., one standard drink is roughly 14 grams (about 0.6 fl oz) of pure alcohol, for example a 12 oz beer at 5% ABV, a 5 oz glass of wine at 12% ABV, or a 1.5 oz shot of 40% liquor.
Can I rely on this to drive?
No. Individual variation is large and the stakes are deadly. If you have consumed alcohol, arrange a ride. The only safe BAC for driving is 0.00.
What raises my BAC fastest?
Drinking quickly, on an empty stomach, and at lower body weight. Food slows absorption but doesn’t prevent intoxication.
Can I use this to decide if I can drive?
No — never. This calculator gives a rough statistical estimate, not a measurement of your actual BAC or your ability to drive safely. Real impairment depends on far more than the number on this screen, and being under 0.08% does not mean you are unaffected or legal to drive everywhere. If you have had any alcohol, arrange another way home.
What is a “standard drink”?
In the U.S., one standard drink is defined as roughly 14 grams (about 0.6 fl oz) of pure alcohol — for example, a 12 oz beer at 5% ABV, a 5 oz glass of wine at 12% ABV, or a 1.5 oz shot of 40% liquor. Use the Size + ABV% mode if your actual drinks differ from these defaults.
Why do legal limits vary?
The 0.08% limit applies to most U.S. drivers, but commercial/CDL drivers face a stricter 0.04% limit, and most states apply zero-tolerance or near-zero limits (commonly 0.00–0.02%) to drivers under 21. Limits also differ outside the U.S. Check your state or country’s specific law rather than relying on this general reference.