Alcohol by Weight is a measurement term used in the United States to legally regulate and tax alcoholic beverages. It is expressed as a percentage of total mass.
In some localities, breweries print the abw (rather than abv) on beverage containers, particularly on low-point versions of popular domestic beer brands. Because alcohol is less dense than the water component of the beverage, alcohol percentage by weight is only 4/5 of the alcohol percentage by volume (e.g., 3.2% abw = 4.0% abv), which has caused confusion among consumers more familiar with the worldwide standard of Alcohol by Volume.