Alcohol Proof & Alcohol by Volume: Definitions, Explanation

Alcohol proof. What is it? Is it different in different countries? How did it get that name? You’ve come to the right place for answers.


I.   Gunpowder Test

II.  Alcohol Proof Varies

III. Alcohol Equivalence

IV.  Cullen-Harrison

V.   Resources

I. Gunpowder Test

So what’s alcohol proof? It dates back to the early 1700s. People measured the alcohol in distilled spirits (liquor) by using gunpowsder. That is, they would “prove” the beverage acceptable.

To do this they poured some on gunpowder and lit it. If it burned steadily with a blue flame, it was considered “proof.”  If it did not burn, it was “underproof.” That is, unacceptable. And if it burned too quickly it was “overproof.”


Pure alcohol (200 proof alcohol) rarely exists outside a lab. That’s because if pure alcohol is open to the air, it will absorb moisture from the atmosphere. Thus it will self-dilute down to about 194 proof. 

II. Alcohol Proof Varies

United Kingdom

In the UK 100 alcohol proof equals 57.1% ethanol by volume. The gunpowder test is the origin of this definition of proof.

United States

In the US, alcohol proof is double the percentage of alcohol in a solution. That’s when the solution is at 60 degrees Fahrenheit. Or 15.6 degrees Celsius. Thus, 150 proof would be 75% alcohol and 100 proof would be 50% alcohol.


In France, alcohol content is in degrees Gay-Lussac (GL). A tech tests the solution with a hydrometer. Then the person expresses alcohol strength as parts of alcohol per 100 parts of the mixture. Thus, a spirit with 40% alcohol by volume equals 40 degrees GL.


The International Organization of Legal Metrology recommends how to measure alcohol strength. A tech distills away all the alcohol, condenses it, and weighs it. The person then expresses the results as a percentage of alcohol by weight (ABW).

Or the tech measures the volume of alcohol distilled and expresses it as a percentage of alcohol by volume (ABV). The person performs the measurement at 20 degrees Celsius or 68 degrees Fahrenheit. Dividing ABW by .079 converts it to ABV.

III. Alcohol Equivalence

alcohol proofThe alcohol proof of standard drinks of beer, wine and spirits (liquor) differ. Yet each contain an equivalent amount of alcohol. That is, 0.6 “pure” ounce each.

This fact is very important. People tend to fool themselves. They don’t know that standard servings of beer, wine, and spirits have the same amount of “real” alcohol. In fact, they’re all the same to a breath tester.

               More Trivia!

Mississippi had state-wide prohibition of all alcoholic beverages for one-third of a century after the repeal of National Prohibition. In fact, hundreds of prohibition or dry counties exist across the US. And they make up almost 10% of its area.

IV. Cullen-Harrison

Congress passed the Cullen-Harrison “non-intoxicating beverage act” as the repeal of Prohibition neared. The act raised “non-intoxicating liquors” from 0.5% to 4% ABV (3.2% ABW).

This legalized low alcohol proof beverages. But states could keep their own prohibition. As a result, 20 states and DC began permitting the sale of low proof alcoholic beverages. They did so on April 7, 1933. That’s when the law became effective.

The 21st Amendment repealed the 18th Amendment (and National Prohibition) on December 5, 1933.  Of course, Repeal made the Cullen-Harrison Act moot. But the 21st Amendment gives states the right to define and regulate alcoholic beverages within their borders.

Today, six states continue to use the old Cullen-Harrison definition. That is, that 3.2% ABW or less are “non-intoxicating.” They are Colorado, Kansas, Minnesota, Missouri, Oklahoma, and Utah.

V. Resources: Alcohol Proof



    • Inter Cent Alco Pol. Lower Alcohol Proof Beverages. Wash: The Center, Rep #19.


    • At this point, you now know much more about alcohol proof than most people!