The average urine test can detect alcohol between 12 and 48 hours after drinking. More advanced testing can measure alcohol in the urine 80 hours after you drink. Breath tests for alcohol can detect alcohol within a shorter time frame. This is about 24 hours on average.
Most of the alcohol consumed is metabolized in the liver, but the small quantity that remains unmetabolized permits alcohol concentration to be measured in breath and urine. The liver can metabolize only a certain amount of alcohol per hour, regardless of the amount that has been consumed.