# Why is 40% alcohol called 80 proof?

if something is 20% alcohol it’s 40 proof, etc. See below proof (alcoholic) In the United States, the proof of an alcoholic beverage is twice its alcohol content expressed as percentage by volume at 60°F. So an 80-proof whiskey is 40% alcohol. Recently the United States has begun to label bottles containing wine and spiriits with the percentage of alcohol by volume, instead of proof. In Europe a different proof system, called Gay-Lussac, is used; it is also the percentage of alcohol by volume, which is half the American proof. The European Union has adopted Gay-Lussac proof as its standard. In Great Britain the situation is much more complicated. A distilled spirit was originally “proved” by one of several methods. One method involved dissolving gunpowder in the spirit and trying to ignite it. If it wouldn’t burn, there was too much water. If it burned evenly and steadily, the spirit was “proven.” Later a legal standard for proof spirit was defined: half rainwater and half spirit prove