What primarily measures the level of alcohol in a person's system?

The level of alcohol in a person's system is primarily measured by Blood Alcohol Concentration (BAC). BAC indicates the percentage of alcohol present in a person’s bloodstream and is typically expressed as a ratio. For example, a BAC of 0.08% means that there are 0.08 grams of alcohol for every 100 milliliters of blood. This measurement is widely used in law enforcement and medical contexts to assess impairment due to alcohol consumption.

BAC is the most direct and scientifically accepted method for quantifying the effects of alcohol on physical and cognitive functions, which is critical in various situations, such as driving under the influence assessments. In contrast, body weight, while it may influence an individual's BAC, is not a direct measurement of alcohol levels. Similarly, urine analysis can provide information about alcohol consumption but may not reflect current BAC due to metabolism and elimination rates. Physical fitness tests do not measure alcohol levels at all, making them irrelevant in this context. Thus, BAC remains the standard measure for assessing the level of alcohol in a person's system.