# Alcoholic proof

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Alcohol proof is a measure of how much alcohol (ethanol) is contained in an alcoholic beverage. The term was originally used in the United Kingdom and was defined as 7/4 times the alcohol by volume (abv). The UK now uses the abv standard instead of alcohol proof. In the United States, alcoholic proof is defined as twice the percentage of abv. The measurement of alcohol content and the statement of this content on the bottle labels of distilled beverages, also called liquors or spirits, is regulated by law[where?]. The purpose of the regulation is to provide pertinent information to the consumer.

## Contents

### History

In the 18th century and until 1 January 1980, the United Kingdom defined alcohol content in terms of “proof spirit”, which was defined as the most dilute spirit that would sustain combustion of gunpowder.[1] The term originated in the 18th century, when payments to British sailors included rations of rum. To ensure that the rum had not been watered down, it was “proofed” by dousing gunpowder in it, then tested to see if the gunpowder would ignite. If it did not, then the rum contained too much water and was considered to be “under proof”. It was found that gunpowder would not burn in rum that contained less than 57.15% abv. Therefore, rum that contained this percentage of alcohol was defined to have "100 degrees proof".

An alcohol content of 57.15% abv is very close to a 4:7 ratio of alcohol to the total volume of the liquid. Thus, the definition amounted to declaring that (4÷7) × 175 = 100 degrees proof spirit. From this it followed that pure, 100% alcohol had (7÷7) × 175 = 175 degrees proof spirit, and that rum containing 50% abv had (3.5÷7) × 175 = 87.5 degrees proof spirit. To convert the percentage of abv to degrees proof spirit, it was only necessary to multiply the percentage by 1.75.

The use of "proof" as a measure of alcohol content is now mostly historical. Today, liquor is sold with labels that state its alcohol content as its percentage of alcohol by volume (abv). United States law requires that liquor labels must state the percentage of alcohol by volume. The proof number may also be placed on the label, provided that it is close to the abv number.[2]