Blood Alcohol Content (BAC) is a measurement of the concentration of alcohol in a person's bloodstream, expressed as a percentage. In Canada, it is illegal to drive with a BAC of 0.08% or higher, though many provinces have additional penalties starting at 0.05%. BAC is influenced by factors including the amount of alcohol consumed, body weight, time elapsed, food consumption, and individual metabolism. Police use breathalyzers to estimate BAC during roadside stops. Understanding BAC helps people make responsible decisions about drinking and driving—even BAC levels below the legal limit impair judgment and reaction time.