What is 100% alcohol?
Michael King
Updated on March 15, 2026
Thus pure 100% alcohol will have 100×( 7⁄4) = 175 proof, and a spirit containing 40% ABV will have 40×( 7⁄4) = 70 proof. The proof system in the United States was established around 1848 and was based on percent alcohol rather than specific gravity. Fifty percent alcohol by volume was defined as 100 proof.