The alcohol in a typical pint of beer will be broken down in about 3 hours. It works pro-rata, so 2 pints - 6 hours, etc. There are other factors at play too. Your size, whether the alcohol was consumed on an empty stomach, or whether it took time to be taken up, but the basic calculation is pretty sound. Three pints of beer in the evening - not unusual in an English pub setting - would still make you unfit to drive the following morning. Scary huh?