IBU stands for International Bitterness Units, which is a scale used to gauge the level of bitterness in beer. Specifically, IBUs measure the parts per million of isohumulone from hops in a beer, which gives beer bitterness. The IBU scale can range from 0 to 120+, but at this point, the human tongue can’t taste any more bitterness. The IBU scale was invented because it felt important to measure how bitter a beer was, and the assignment of numbers helps with conceptual understanding. However, IBU isn’t the only indicator of how a beer may taste, as malt/grain character and sweetness can balance out bitterness in a beer.