How to Calculate Blood Alcohol Level

While the only 100 percent accurate method to determine your blood alcohol level requires a lab test, this formula can give you a general idea of how much alcohol is in your bloodstream.


  • : Don't drink unless you're of legal age. Drink responsibly, and never drink and drive.
  • Step 1: Determine the number of drinks Determine how many drinks you've had. A standard drink in the U.S. contains .6 ounces of pure alcohol.
  • TIP: Generally, .6 ounces of pure alcohol is found in 12 ounces of beer, 8 ounces of malt liquor, 5 ounces -- or one standard glass -- of wine, or 1.5 ounces -- one shot -- of 80-proof liquor.
  • Step 2: Multiply by .025 Multiply the number of standard drinks you had by .025. This will give an approximation of your percent blood alcohol.
  • TIP: Remember that men metabolize alcohol faster than women, and that people who weigh more absorb alcohol faster.
  • Step 3: Determine the time since your last drink Determine the amount of time that has passed since you took your last drink of alcohol.
  • Step 4: Subtract .025 percent Subtract .025 percent for each full hour that passed since your last drink. If 2 hours have passed since you finished your third drink, subtract .05 from 0.075 to determine an approximate blood alcohol level of .025 percent.
  • Step 5: Wait To be safe, wait to drive until you calculate your blood level is back near 0. Wait at least an additional half hour if you are a woman or you weigh less than 150 pounds.
  • FACT: Research has shown that youths who use alcohol before age 15 are 5 times more likely to become alcohol-dependent than adults who begin drinking at age 21.

You Will Need

  • Number of drinks
  • Math skills
  • Gender and weight considerations
  • Time

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