Regardless of your size and weight, it takes your liver about hour(s) to remove one drink from your system.

Alcohol is metabolized (broken down) by the body (the liver), where enzymes break down the alcohol. at a rate of 0.016% per hour.
Regardless of your size and weight every person metabolizes drinks at the pace.
BAC stands for blood alcohol concentration.Is it percentage of alcohol per mass of blood. For every hour you are not drinking, .015 of the alcohol in your body is being metabolized and disappearing from your body. 
Let assume the drink has 0.015 alcohol. Then it takes your liver about one hour to remove one drink from your system.