Addiction Alcohol Use Print How Blood Alcohol Concentration (BAC) Impairs Your Body and Brain By Elizabeth Hartney, BSc., MSc., MA, PhD Elizabeth Hartney, BSc, MSc, MA, PhD is a psychologist, professor, and Director of the Centre for Health Leadership and Research at Royal Roads University, Canada. Learn about our editorial process Elizabeth Hartney, BSc., MSc., MA, PhD Updated on September 19, 2019 DarrenMower /E+ / Getty Images More in Addiction Alcohol Use Binge Drinking Withdrawal and Relapse Children of Alcoholics Drunk Driving Addictive Behaviors Drug Use Nicotine Use Coping and Recovery Blood alcohol concentration (BAC) is a measurement of the percentage of alcohol that's in your bloodstream after you've been drinking. Your BAC, rather than the exact amount of alcohol you've consumed, will determine the effects the alcohol will have on you. In all states, the legal limit to drive is any number below .08. Factors That Affect BAC Body sizeBiological sexPhysical conditionMedications you takeWhat you've eaten (and when)How much sleep you've hadAlcohol content of your drinks As BAC increases, so does the level of alcohol-related impairment you will experience. While a breathalyzer gives fast results and is often used by police officers who suspect that an individual has been driving while drunk, it is not as accurate as measuring the amount of alcohol in your blood. How BAC Is Calculated To calculate BAC, the amount of alcohol in the bloodstream is measured in milligrams (mg) of alcohol per 100 milliliters (ml) of blood. It is usually expressed as a decimal such as 0.08 or 0.15. For example, a BAC of 0.10% means that an individual’s blood supply contains one part alcohol for every 1,000 parts blood. How BAC Affects Impairment The Centers for Disease Control and Prevention provides the following chart which illustrates how alcohol consumption and BAC can impact behavior, judgment, physiology, and driving ability. BAC Standard Drink Equivalent Typical Effects Predicted Effects on Driving 0.02% ~2 alcoholic drinks Some loss of judgment, relaxation, slight body warmth, altered mood Decline in visual functions (rapid tracking of moving target) and ability to perform two tasks at the same time (divided attention) 0.05% ~3 alcoholic drinks Exaggerated behavior, loss of small-muscle control (e.g., focusing your eyes), impaired judgment, lowered alertness, release of inhibition Reduced coordination, reduced ability to track moving objects, difficulty steering, reduced response to emergency driving situations 0.08% ~4 alcoholic drinks Poor muscle coordination (e.g., balance, speech, vision, reaction time, hearing), difficulty detecting danger, impaired judgment, self-control, reasoning, and memory Loss of concentration, short-term memory loss, impaired speed control, reduced information processing capability (e.g., signal detection, visual search), impaired perception 0.10% ~4 alcoholic drinks Clear deterioration of reaction time and control, slurred speech, poor coordination, slowed thinking Reduced ability to maintain lane position and brake appropriately 0.15% ~7 alcoholic drinks Far less muscle control than normal, potential for vomiting, major loss of balance Substantial impairment in vehicle control, attention to driving task, and visual and auditory processing The number of drinks listed represents the approximate amount of alcohol that a 160-pound man would need to drink in one hour to reach the listed BAC in each category. A standard drink is equal to 14 grams (0.6 ounces) of pure alcohol. Generally, this amount of pure alcohol is found in: 12 ounces of beer (5% alcohol content)8 ounces of malt liquor (7% alcohol content)5 ounces of wine (12% alcohol content)1.5 ounces or a “shot” of 80-proof (40% alcohol content) distilled spirits or liquor (e.g., gin, rum, vodka, whiskey) Your blood alcohol level results may be given in different ways, including the percentage of blood alcohol content (BAC). Typical results include: Sober: 0.0% BACLegally intoxicated: .08% BACVery impaired: .08–0.40% BAC. You may have difficulty walking and speaking. Other symptoms may include confusion, nausea, and drowsiness.At risk for serious complications: Above .40% BAC. An individual with this blood alcohol level may be at risk for coma or death. A blood alcohol test is only accurate within 6 to 12 hours after your last drink. If you have concerns about your results, you may want to talk to a health care provider and/or a lawyer. How Blood Alcohol Content Works Was this page helpful? Thanks for your feedback! Learn the best ways to manage stress and negativity in your life. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Kriikku P, Wilhelm L, Jenckel S, et al. Comparison of breath-alcohol screening test results with venous blood alcohol concentration in suspected drunken drivers. Forensic Sci Int. 2014;239:57-61. doi: 10.1016/j.forsciint.2014.03.019 Centers for Disease Control and Prevention. Impaired Driving: Get the Facts. Updated March 22, 2019.