Buzz
Anyone who's ever scrutinized bottles in their parent's liquor cabinet knows that a liquor's proof is double its alcohol by volume percentage. Why use this 0-200 scale? It all goes back to history.
The term 'proof' in relation to alcohol dates back to a time when traders had to literally prove the authenticity of their spirits. William B. Jensen from the University of Cincinnati explains that, in 16th century England, merchants would soak gunpowder pellets in liquor to test its strength. If the wet gunpowder could still be ignited, the alcohol content was deemed high enough to be taxed at a higher rate, and if not, the liquor would be taxed less.
Though the concept of 'proof' stuck around, its origin in America diverged from gunpowder testing. By 1848, 50% alcohol by volume became the standard, with 100 proof being its corresponding number. Therefore, the proof of liquor is always twice its ABV percentage.
Other countries use different systems to measure proof. For instance, in 1816, the U.K. adopted a gravity-based method. According to the Customs and Excise Act, 100 proof liquors are those where the spirits weigh 12/13 of the weight of an equal volume of distilled water at 51° F (11° C). This results in a proof value that's roughly 1.75 times the alcohol by volume percentage. All this math might make someone want to reach for a drink themselves.
