What Is Blood Alcohol Content (BAC)?
BAC is the concentration of alcohol in your bloodstream, expressed as a percentage by weight. A BAC of 0.08% means 0.08 grams of pure alcohol per 100 mL of blood. It's the standard measure used by law enforcement, courts, and toxicologists to quantify intoxication. In the United States, 0.08% is the legal driving limit for adults 21 and over — and impairment begins much earlier, around 0.02-0.03%.
How BAC Is Calculated (The Widmark Formula)
Developed by Swedish physiologist Erik Widmark in the 1930s, the Widmark formula is the gold-standard estimation method used worldwide:
BAC = (Alcohol in grams ÷ (Body weight in grams × r)) × 100 − (0.015 × Hours)
- r (Widmark factor) — 0.68 for men, 0.55 for women (reflects body water distribution)
- 0.015%/hour — the average rate the liver metabolizes alcohol (constant for everyone)
- Alcohol in grams — 1 US standard drink = 14g pure alcohol
The calculator above does this math for you, then shows impairment level, time to sober, and time to reach the 0.08% legal limit.
What Counts as One Standard Drink?
One US standard drink contains 14 grams (0.6 oz) of pure alcohol:
| Beverage | Typical pour | ABV | Standard drinks |
|---|---|---|---|
| Regular beer | 12 oz (355 ml) | ~5% | 1 |
| Wine | 5 oz (148 ml) | ~12% | 1 |
| Spirits (shot) | 1.5 oz (44 ml) | ~40% | 1 |
| Craft beer | 16 oz pint | ~7% | 1.5 |
| Restaurant wine pour | 8 oz | ~12% | 1.6 |
| Long Island Iced Tea | — | — | 3-4 |
Key trap: craft beers and cocktails often contain more than one standard drink — that's why people underestimate their BAC. When in doubt, round up.
BAC Effects by Level
| BAC | Typical effects | Legal status (US) |
|---|---|---|
| 0.01 - 0.03% | Slight relaxation, mild mood lift | Legal |
| 0.04 - 0.06% | Lowered inhibitions, mild impairment | Legal but impaired |
| 0.07 - 0.09% | Impaired balance, slower reaction | DUI at 0.08% |
| 0.10 - 0.15% | Slurred speech, poor coordination | Illegal everywhere |
| 0.16 - 0.30% | Confusion, memory blackout risk | Illegal |
| 0.30%+ | Unconsciousness risk, respiratory depression | Medical emergency |
Legal BAC Limits by Country
| Country / Region | Driving limit |
|---|---|
| USA (most states) | 0.08% |
| USA (commercial drivers) | 0.04% |
| USA (under 21) | 0.00 - 0.02% (zero tolerance) |
| UK / Canada | 0.08% |
| Australia | 0.05% |
| Most of Europe | 0.05% |
| Sweden / Norway | 0.02% |
How Your BAC Changes Over Time
Once you stop drinking, your blood alcohol content doesn't stay at its peak — it falls on a steady, predictable line as your liver processes the alcohol. Understanding this BAC over time curve is what tells you how long until you're sober enough to drive. Your body eliminates alcohol at a roughly constant rate, so your BAC drops by about 0.015% every hour until it reaches zero. The timeline in the calculator above shows this exact hour-by-hour projection for your situation.
Two things matter most when reading the curve: your peak BAC (how high you got, set by weight and drinks) and how long ago you started. Everything after that is just that steady hourly decline — which is why "sobering up" is entirely a matter of time, not tricks.
How long does it take for BAC to reach zero?
On average, it takes about 5-7 hours for a typical night of drinking to bring your blood alcohol content back to 0.00%. The math is simple: divide your current BAC by 0.015 (the hourly elimination rate). A BAC of 0.08% takes roughly 5.3 hours; a BAC of 0.10% takes about 6.7 hours. Use the timeline above to see your personal estimate hour by hour.
How much does BAC drop per hour?
Most people metabolize alcohol at about 0.015% BAC per hour, though individual rates range from roughly 0.010% to 0.025% depending on your metabolism, liver health, and genetics. Because the rate is fairly constant, your BAC over time follows a steady downward line rather than dropping suddenly — which is why a 0.08% reading tonight still means a 0.05% reading roughly two hours later.
When can I drive after drinking?
You're legally clear to drive once your BAC is below the limit in your area — 0.08% in the US. If your estimated BAC is 0.10%, that means waiting about 1.3 hours (0.02 ÷ 0.015) to reach 0.08%. For the safest choice, wait until your estimated BAC reaches 0.00% before getting behind the wheel, and never rely on an estimate to make that call.
Does drinking water or coffee sober you up faster?
No. Coffee, water, cold showers, and food may make you feel more awake, but none of them lower your blood alcohol content — only your liver can do that, at its fixed rate of about 0.015% per hour. That's why the only reliable answer to "how long until I'm sober" is to watch the BAC-over-time curve and give your body the hours it needs.
How long does alcohol stay in your system?
This depends on the test, not just your BAC. Alcohol is detectable on the breath for about 12-24 hours, in urine for 12-48 hours (up to 80 hours with sensitive EtG tests), and in hair for up to 90 days. Your blood alcohol concentration itself, however, returns to zero within hours of your last drink — the timeline above projects exactly when.
Frequently Asked Questions
What is a normal BAC?
It should be 0.00% when not drinking. Below 0.05% causes subtle effects; 0.08% is the US legal limit; 0.15%+ causes severe impairment.
How long does it take to get sober?
The body eliminates ~0.015% BAC per hour. Divide your BAC by 0.015 for time to zero. Coffee, showers, and food don't speed it up — only time.
What is one standard drink?
14g of pure alcohol: 12 oz beer (5%), 5 oz wine (12%), or 1.5 oz spirits (40%). Craft beers and cocktails often count as more.
Why do women get higher BAC?
Women have less body water per weight, so the same drinks produce roughly 24% higher BAC. The Widmark factor accounts for this.
Can I speed up alcohol metabolism?
No — the liver metabolizes at a constant ~0.015%/hour. Coffee, water, exercise, and food don't help. Only time lowers BAC.
Is this calculator accurate?
It's an estimate based on the Widmark formula. Individual variation (food, medication, liver health, genetics) is significant. Only breathalyzer/blood tests are legally recognized.
This calculator is one of four tools in our Everyday Health guide, which also covers daily hydration, hair growth, and how body weight changes your BAC.
Methodology & sources: Widmark formula (Erik Widmark, 1930s); standard drink definition per US NIAAA (14g pure alcohol); metabolism rate ~0.015%/hr per NIAAA; legal limits per NHTSA and international standards. This tool is for educational purposes only — never use it to decide whether to drive.