How is alcohol content expressed in the USA?

In the USA, alcohol content is primarily expressed using the degree proof system, which is a measurement that effectively doubles the percentage of alcohol by volume (ABV). For example, if a spirit has an ABV of 40%, its proof would be 80 degrees. This system is unique to a few countries, with the USA being one of the most notable examples of its use.

While other countries and regions typically use percentage by volume to indicate alcohol content, the proof system in the USA helps to provide a more immediate sense of how strong a beverage is, as it gives a whole number value that is often easier for consumers to perceive when making choices about alcohol consumption.

In comparison, percentage by volume directly states the concentration of alcohol in a given volume of liquid, standard drink measurement helps consumers understand their intake in terms of serving sizes, and alcohol by weight, which is measured differently and less commonly used in practice, is not a standard measure for consumers in the USA.