Depending upon one's country, there is a definition of "Standard Drink Equivalents" (SDE) or "Units," which relate to how much alcohol is consumed.

The National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines a SDE in the United States to be a drink that contains 14 grams of alcohol (ethanol).

To calculate SDE's, the user must enter the quantity consumed and the concentration of alcohol (ethanol) in that drink.

The formula for the U.S.:

• SDE = (mL consumed × fraction ethanol × 0.8 grams/mL)/14

For other countries, the denominator will be altered based upon how many grams are indicated in an SDE or "Unit."

References:

• International Center for Alcohol Policies (ICAP). What are "standard drinks"? http://www.icap.org/policyissues/drinkingguidelines/standarddrinks . Updated May, 2009. Last accessed May 27, 2013.
• Public Health Agency of Canada. Management Guidelines for the HCV/HIV Co-Infected Adult. http://www.phac-aspc.gc.ca/hepc/pubs/gdhcvhivadlt-ldvhcvihadlt/index-eng.php . Updated 05 Feb, 2002. Last accessed May 27, 2013.
• United States Department of Agriculture (USDA). Dietary Guidelines for Americans 2005: Alcoholic Beverages. http://www.health.gov/dietaryguidelines/dga2005/document/html/chapter9.htm . Updated July 09, 2008. Last accessed May 27, 2013.