What BAC is — and the one thing this calculator is not for
Blood alcohol content is the percentage of your blood that is alcohol: a BAC of 0.08% means 8 parts per 10,000. It's the number breathalysers approximate, the number laws are written around, and the number this page estimates from your drinks, body, and the clock.
Before the math, the disclaimer that actually matters: no calculator can tell you whether you're safe or legal to drive, and this one doesn't try. Real BAC varies with food, medication, fatigue, and individual metabolism in ways no formula captures — and impairment starts well below any legal limit. If there's any question, the answer is a taxi. What this tool is for: understanding how alcohol math works, pacing an evening, and estimating how long until your body is genuinely clear.
The Widmark formula
Nearly a century old and still the standard, Erik Widmark's equation says: take the grams of alcohol you drank, divide by your body weight times a distribution ratio (about 0.68 for men, 0.55 for women — alcohol distributes into body water, and body composition differs), then subtract what your liver has already cleared, roughly 0.015% per hour.
A worked example: an 82 kg (180 lb) man has three US standard drinks — 42 grams of alcohol — over an evening. Peak BAC comes out near 0.075%. Two hours of metabolism subtracts 0.03, leaving roughly 0.045% — measurably impaired, whatever the legal limit says.
The phrase 'standard drink' is doing heavy lifting there: in the US it means 14 grams of pure alcohol — a 12 oz regular beer, a 5 oz glass of wine, or a 1.5 oz shot of spirits. The IPA in your hand at 8% is closer to two standard drinks than one, and generous home pours are the main reason people's mental count runs low.
What different BAC levels feel like
| BAC | Typical effects |
|---|---|
| 0.02–0.03% | Mild relaxation, slight mood lift |
| 0.05% | Lowered inhibition, measurably slower reactions |
| 0.08% | Clearly impaired coordination and judgment; common legal limit |
| 0.15% | Major impairment, vomiting risk, blackouts possible |
| 0.30%+ | Loss of consciousness; medical emergency territory |
Alcohol poisoning — confusion, vomiting while drowsy, slow or irregular breathing, unresponsiveness — is a call-emergency-services situation, not a sleep-it-off situation.
Sobering up: only time works
The liver clears alcohol at its own fixed pace — roughly one standard drink per hour — and nothing sold, brewed, or believed changes that. Coffee makes an alert drunk person; cold showers make a wet one; food slows absorption if it's eaten before drinking but does nothing after the fact. The calculator's 'time to zero' figure is the honest number: from a heavy night, full clearance often lands the next afternoon, which is why morning-after driving catches so many people out.
Frequently asked questions about BAC
What is blood alcohol content (BAC)?
BAC is the percentage of alcohol in your bloodstream. It rises with drinks consumed, body size, and gender, and falls over time as your liver metabolises alcohol.
What BAC is illegal to drive?
Limits vary by country and state. In many US states the legal limit is 0.08% for drivers 21+. Lower limits apply for commercial drivers and under-21 drivers.
Can I rely on a BAC calculator before driving?
No. Calculators are estimates only. Never drink and drive — use a designated driver, taxi, or rideshare.
How do I use this BAC calculator?
Enter gender, weight, drinks consumed, alcohol percentage, and time elapsed, then click Calculate to see an estimated BAC.
Sources and further reading
- NIH NIAAA — What is a standard drink?
- CDC — About alcohol use and health
- NHTSA — Drunk driving facts and BAC effects
This page is for general information only. BAC estimates cannot determine fitness or legality to drive. If you're concerned about your drinking, the NIAAA and your doctor can help.