BAC Levels and Their Effects
Typical effects by blood alcohol concentration, based on the NHTSA's summary. People with high tolerance may show fewer outward signs at the same BAC, but their driving is still impaired.
| BAC Range | Effects |
|---|---|
| 0.00-0.02% | Little outward effect; some relaxation, altered mood, slight loss of judgment from about 0.02% |
| 0.02-0.05% | Relaxation, lowered alertness, reduced visual function and trouble doing two things at once |
| 0.05-0.08% | Exaggerated behavior, impaired judgment, reduced coordination and slower response in an emergency: driving risk elevated |
| 0.08-0.15% | Poor muscle coordination, slurred speech, slowed thinking, reduced ability to keep a lane and brake properly |
| 0.15-0.30% | Far less muscle control, major loss of balance, vomiting may occur; risk of alcohol poisoning |
| 0.30%+ | Life-threatening: confusion, loss of consciousness, slowed breathing. Call emergency services |
Call 911 (or your local emergency number) if someone cannot be woken, has slow or irregular breathing, is vomiting while drowsy, has seizures, or has blue-tinged or pale skin. These are signs of alcohol overdose. Do not leave them alone to "sleep it off".
The Widmark formula
BAC (%) = alcohol (g) ÷ (body weight (g) × r) × 100 − 0.015 × hours
alcohol (g) = drinks × volume (ml) × ABV × 0.789
r = 0.68 for men, 0.55 for women
Erik Widmark published the method in 1932. The factor r is the share of body weight that alcohol spreads into, mostly body water, which is why women and people with more body fat reach a higher BAC from the same drinks. The body then clears alcohol at a roughly steady rate, on average about 0.015 percentage points an hour, with real rates varying from person to person.
Worked example. A 60 kg woman drinks two 5 oz glasses of 12% wine. Each glass holds 5 × 29.57 = 147.9 ml × 0.12 = 17.7 ml of alcohol, or 17.7 × 0.789 = 14.0 g. Two glasses: 28.0 g. Peak BAC: 28.0 ÷ (60,000 × 0.55) × 100 = 28.0 ÷ 33,000 × 100 = 0.085%, above the US limit. After 3 hours: 0.085 − 0.045 = 0.040%. Reaching zero takes about 0.085 ÷ 0.015 = 5.7 hours from the first drink.
What counts as one drink?
In the US a standard drink holds 14 grams of pure alcohol, according to the NIAAA: 12 fl oz of regular beer at about 5%, 5 fl oz of wine at about 12%, 1.5 fl oz of 40% spirits, or 8 to 10 fl oz of malt liquor or hard seltzer at about 7%. A UK unit is 8 grams, so one US standard drink is about 1.75 UK units. Many craft beers, large wine glasses and mixed drinks hold far more than one standard drink.
Legal BAC Limits by Country
| Country | Limit (BAC%) | Note |
|---|---|---|
| USA (most states) | 0.08% | 0.04% for commercial drivers; Utah uses 0.05%; under-21 drivers face near-zero limits |
| Canada | 0.08% | Criminal limit; most provinces add sanctions from 0.05% |
| England / Wales | 0.08% | Also Northern Ireland; Scotland has a stricter 0.05% limit |
| Scotland | 0.05% | Stricter than England and Wales |
| Australia | 0.05% | 0.00% for learner and provisional drivers |
| Germany | 0.05% | 0.00% for drivers under 21 and in the probation period |
| France | 0.05% | 0.02% for probationary licences (first 3 years) and bus drivers |
| Spain | 0.05% | 0.03% for new drivers (first 2 years) and professional drivers |
| Netherlands | 0.05% | 0.02% for new drivers (first 5 years) |
| Italy | 0.05% | 0.00% for new drivers (first 3 years) and professional drivers |
| Japan | 0.03% | Very strict enforcement, criminal penalties |
| India | 0.03% | 30 mg per 100 ml of blood, national limit |
| Russia | 0.035% | 0.356 g per liter of blood, allows only for measurement error |
| Sweden | 0.02% | Effectively zero tolerance |
| Norway | 0.02% | Effectively zero tolerance |
| Poland | 0.02% | Criminal offence above 0.05% |
| Ukraine | 0.02% | Strict enforcement |
| China | 0.02% | 0.08% = criminal offence |
| Brazil | 0.00% | Zero tolerance, heavy fines |
| Saudi Arabia | 0.00% | Alcohol prohibited entirely |
| EU (most member states) | 0.05% | Lower limits for novice and professional drivers are common |
Laws change and some countries measure breath rather than blood alcohol. Check the current rules of the country you drive in. Being under the limit does not mean it is safe to drive.
What does not lower BAC
Coffee, cold showers, fresh air and exercise do not speed up the removal of alcohol. Only time does. Eating before drinking slows absorption and lowers the peak, but the alcohol still has to be cleared. You can still be over the limit the morning after a heavy night.