Many countries require their wineries—or wines entering their country—to report to the consumer how much alcohol is in their wine. In the United States, the amount of alcohol is listed on the label as a percentage of the whole bottle of wine. Somewhere on the label in fine print you'll see something like "Alcohol 13.1% by Volume," which means nearly an eighth of the wine is pure alcohol. U.S. law forbids table wines to exceed 14% ABV; otherwise it's considered a dessert wine. A loophole in the law, however, allows for a 1.5% margin of error, so a 12.5% ABV wine could actually be 14% (but never higher). As a general rule, if the label gives an exact percentage (e.g., 13.6%), it's probably a precise measurement.