Serving would be a helpful term, except that servings aren't standardized. Depending on which cereal you buy, a serving ranges from 3/4 of a cup to 1&1/2 cups. The marketing guys are now targeting calories as a selling point so they take their sugar-packed air-ball choco pops and say there's only 110 calories compared to your 120 calorie corn flakes that give you a full cup with less air.