What Is Alcohol Proof?
Alcohol proof is a measure of the alcohol content of a spirit or drink. This calculator uses the United States definition, where proof is exactly twice the percentage of alcohol by volume (ABV). So an 80-proof whiskey contains 40% alcohol by volume. (Note: the historic UK proof system used a different ratio of about 4/7, so this tool applies to US proof.)
How to Use This Calculator
Enter the proof value printed on the bottle and the calculator instantly returns the equivalent ABV percentage. Because the relationship is linear, you simply halve the proof number.
The Formula Explained
The conversion is straightforward:
$$\text{ABV \%} = \dfrac{\text{proof}}{2}$$
This means proof is always double the ABV. To go the other direction, multiply ABV by 2 to get the proof.
Worked Example
Suppose you have a bottle labeled 100 proof. Divide by 2: \(100 / 2 = 50\) % ABV. A common 80-proof vodka works out to \(80 / 2 = 40\) % ABV, and a 151-proof rum is \(151 / 2 = 75.5\) % ABV.
Proof to ABV Conversion Table
In the United States, alcohol proof is exactly twice the percentage alcohol by volume (ABV). To convert, simply divide the proof by 2:
$$\text{ABV} = \frac{\text{Proof}}{2}$$For example, a spirit labeled 80 proof contains 40% ABV. The table below lists common proof values and their exact ABV equivalents.
| Proof (US) | ABV (%) |
|---|---|
| 40 | 20% |
| 80 | 40% |
| 86 | 43% |
| 90 | 45% |
| 100 | 50% |
| 101 | 50.5% |
| 110 | 55% |
| 120 | 60% |
| 151 | 75.5% |
| 190 | 95% |
| 200 | 100% |
Note that this 2:1 relationship is specific to the US system. In the historical British (Imperial) system, 100 proof corresponds to about 57.1% ABV, so US and UK proof values are not interchangeable.
FAQ
Is proof always double the ABV? In the US, yes. The UK historically defined proof differently, so always confirm which system a label uses.
What is the highest possible proof? Pure alcohol is 100% ABV, which equals 200 proof. Most spirits range from 80 to 151 proof.
Why does the US use proof at all? It is a legacy unit from when tax was based on alcohol content. ABV is the modern, internationally standard measure.
