Alcohol proof is a measure of the content of ethanol (alcohol) ...wikipedia - 09 Oct 2015
Alcohol proof is a measure of the content of ethanol (alcohol) in an alcoholic beverage. The term was originally used in the United Kingdom and was equal to about 1.75 times the alcohol by volume (ABV). The UK now uses the ABV standard instead of alcohol proof. In the United States, alcohol proof is defined as twice the percentage of ABV.