What is BAC?
Blood alcohol concentration (BAC) is the amount of alcohol in your blood. It rises as you drink, falls slowly as your liver clears about 0.015% per hour, and decides how impaired you are.
In India the legal limit for driving is 0.03% (30 mg per 100 ml of blood). But driving skills are affected by the first drink — the only safe amount when driving is none.
How it is calculated
Alcohol (g) = volume (ml) × ABV% × 0.789
BAC % = alcohol (g) ÷ (r × body weight g) × 100 − 0.015 × hours
The Widmark factor r is about 0.68 for men and 0.55 for women, because women have less body water.
Worked example
80 kg man, two 330 ml beers at 5%
- Alcohol
- 26 g
- Peak BAC
- 0.048%
- After 2 hours
- 0.018%
- Time to reach 0.00%
- about 3.2 hours
Effects at different BAC levels
| BAC | Typical effect |
|---|---|
| 0.00–0.03% | Little effect: Subtle changes, but impairment is already possible. |
| 0.03–0.06% | Mild euphoria: Relaxed, reduced concentration and judgement. |
| 0.06–0.10% | Impaired: Poor reasoning, balance and depth perception. |
| 0.10–0.20% | Clearly intoxicated: Slurred speech, slow reflexes, poor coordination. |
| 0.20–0.30% | Severe: Confusion, vomiting, memory blackouts. |
Never drive, ride or operate machinery after drinking. This is an estimate only — real BAC varies with food, health, medicines and how fast you drink.