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BAC Basics

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What is BAC?

Blood Alcohol Concentration (BAC) is a measure of the amount of alcohol in a person's blood stream.

BAC levels are affected by many things; however, the following are the most significant factors influencing a person's BAC level:

  • Quantity of alcohol consumed
  • Rate of consumption
  • Body weight and composition
  • Biological sex

Biology dictates a great deal of our response to alcohol; men and women are significantly different. If a man and a woman of the same weight drink the same amount of alcohol, the woman will have a higher BAC. Why? Women are usually smaller, have more body fat, and have a lower body water content than men. Hormonal differences, especially due to a woman's menstrual cycle, and different levels of digestive enzymes that metabolize alcohol also influence women's BAC. All of these factors contribute to higher concentrations of alcohol in a woman's system even if she is drinking the same amount as a man.

Additionally, the following factors may also influence how quickly a person's BAC level rises and/or how impaired they become:

  • Amount of food consumed
  • Hydration level
  • Other substances consumed (prescription and over-the-counter medication; illicit drugs)
  • Fatigue/energy level
  • Health status/illness
  • Mood and mindset


What is a standard drink?


Source: Centers for Disease Control & Prevention


A standard drink equals:

  • a 12 oz. bottle or can of beer (~5% alcohol) or
  • a 4-5 oz. glass of wine (~12% alcohol) or
  • a 8 oz. bottle of a malt beverage--"hard" lemondade/tea; etc. (~ 7% alcohol) or
  • a 1.5 oz. shot of hard alcohol (~ 80% alcohol) or
  • a mixed drink containing only one 1.5 oz. shot (~80% alcohol) of hard alcohol

Many mixed drinks contain more than one shot of alcohol. A Long Island Iced Tea, for example, can have 4-5 (or more!) shots of alcohol.

The concentration of alcohol in a beverage is usually stated as the percentage of alcohol by volume (ABV) or as proof. Alcohol proof is twice the percentage of alcohol by volume. For example, hard alcohol which is 80 proof is 40% alcohol by volume. A higher proof indicates a higher volume of alcohol per serviing. As a result, the standard serving size would be smaller.

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