What does BAC mean?
BAC stands for blood alcohol concentration. It describes the amount of alcohol in a person’s blood. In the United States, BAC is commonly expressed as grams of alcohol per deciliter of blood (g/dL); a result of 0.08% corresponds to 0.08 g/dL.
BAC is not the same thing as how someone feels. Alcohol can affect judgment, attention, coordination, and reaction time before a person recognizes impairment.
How is BAC measured?
A BAC value is measured with a properly administered breath test or blood test. An online BAC calculator is different: it estimates a range from information such as the amount of pure alcohol, body weight, sex used in a formula, and elapsed time. It cannot account for every factor that changes absorption and metabolism.
What can affect blood alcohol concentration?
- How much alcohol: more pure alcohol generally raises BAC.
- How quickly it is consumed: drinking over a shorter period can produce a higher BAC.
- Body size and composition: these affect how alcohol is distributed.
- Food, timing, health, medication, and individual metabolism: each can change absorption or how the body processes alcohol.
Because these variables differ from person to person and moment to moment, only a breath or blood test can measure actual BAC.
BAC and driving
Legal limits, measurement methods, and penalties vary by country, state, driver category, and circumstances. More importantly, impairment can begin below a legal limit. Do not use a calculator, a rule of thumb, coffee, food, water, or time estimates as a reason to drive after drinking.
Use the right tool for the question
- To estimate alcohol in a serving, use the Standard Drinks Calculator.
- To check a bottle, can, or pint, use the Standard Drinks per Container Calculator.
- To see an educational model across future hours, use BAC Calculator Over Time.
- To convert a BAC percentage into other units, use BAC Conversion.
- To learn how the BAC calculation works, see our methodology and limits.