What does blood alcohol content measure?

Blood alcohol content (BAC) measures the percentage of alcohol present in a person's bloodstream. This measurement reflects how much alcohol is circulating in the blood, which is crucial for understanding a person's level of intoxication and for legal regulations regarding driving under the influence. A higher BAC indicates a higher concentration of alcohol, which can impair physical and cognitive functions. Knowing this percentage is essential in law enforcement and public safety to assess potential risks and make informed decisions about legal consequences for individuals.

The other options relate to different physiological measures that do not pertain to alcohol or its effects on the body. For instance, the volume of blood in the body is a measure of fluid levels, while the rate of blood circulation pertains to how quickly blood moves through the body, and hydration levels indicate water content but have no relevance to alcohol concentration. All these factors are important in their own right, but they do not relate specifically to the measurement of alcohol in the bloodstream like BAC does.