A 1-pound package of brown sugar contains 2.5 cups. A 2-pound bag contains 4 cups, and a 4-pound bag contains 8 cups. Most sugar manufactures base cup measurements on firmly packed brown sugar.
Packing brown sugar involves filling the measuring cup with brown sugar and pressing it down firmly using the back of a spoon or fingers. This process should be continued until the required amount is packed. Most recipes that include brown sugar indicate whether the measurement is based on a light or firm packing technique. Brown sugar needs to be packed when measuring, as its consistency naturally creates air pockets that need to be removed to achieve the required amount for a recipe.