Proof

Proof is a way of stating how much alcohol a spirit contains, and in the United States it is set at exactly double the alcohol by volume, or ABV, percentage. A spirit labeled 80 proof is 40 percent ABV, and one labeled 100 proof is 50 percent ABV. Most countries outside the US simply use ABV directly rather than a separate proof scale.

The number matters for more than just strength, since higher proof spirits carry more flavor and aroma into a mixed drink and stand up better to dilution from ice, which is part of why some cocktail recipes specifically call for a higher proof bottling of a base spirit. Lower proof options can taste thin or get lost once shaken or stirred with ice and other ingredients.

When comparing bottles for a specific recipe, checking the proof rather than assuming all versions of a spirit are equivalent avoids drinks that turn out weaker or more diluted than intended. A common point of confusion is assuming proof and ABV are the same number, when in the American system proof is always twice the ABV figure printed nearby on the label.