What does it mean when a bottle of alcohol says 60 percent proof?

The term "proof" in relation to alcohol refers to the alcohol content by volume (ABV) in certain countries, including the United States. It is a historical measurement that dates back to the 16th century when gunpowder was tested for its strength by soaking it in alcohol and setting it alight. The higher the alcohol content, the more gunpowder would ignite and the "stronger" the proof.

When a bottle of alcohol says 60 percent proof, it means that it contains 60 percent alcohol by volume. To convert proof to ABV, you need to divide the proof number by two. So, 60 percent proof is equivalent to 30 percent ABV.

In some other countries, such as the United Kingdom, the alcohol content of beverages is usually indicated in ABV rather than proof.