Alcoholic proof is a measure of how much
ethanol is in an
alcoholic beverage, and is approximately twice the percentage of
alcohol by volume (
ABV, the unit that is commonly used at present).
The European Union follows the recommendation of the International Organization of Legal Metrology (OIML) which states percentage of alcohol by volume (ABV) at 20 °C.
Britain originally specified alcohol content in terms of proof spirit, originally defined as the most dilute spirit which would sustain combustion of gunpowder. In this system, spirit of 100 degrees proof contains 57.1% alcohol by volume or 49.28% alcohol by weight at 51 °F (10.6 °C) and is equivalent to 114.2 proof in the USA. Pure ethanol is 175.25 degrees proof, or more strictly is 75.25 degrees over proof.[1] From the 1740s until 1816 Customs and Excise and London brewers and distillers used Clarke's hydrometer to measure proof. From 1816 the Sikes hydrometer was used to measure degrees proof. Officially the Customs and Excise Act of 1952 defined "spirits of proof strength" (or proof spirits)
Britain now uses the EU ABV standard.
