Self-rising flour is flour that has baking powder and salt added, and is used in recipes for quick breads and cakes. Self-rising flour is convenient for bakers who regularly bake from recipes calling for it. For most home bakers and cooks, however, it's better to buy all-purpose flour and add the needed baking powder and salt, as the additional ingredients cannot be removed from self-rising flour when you don't need the additional salt or chemical leavener. All-purpose flour has slightly more protein than self-rising flour, but the difference is usually negligible.
Multiply the number of cups of flour by 1 1/4. This will be the number of teaspoons of baking powder to add to the all-purpose flour. For example, if your recipe calls for 3 cups of self-rising flour, use 3 cups of all-purpose flour and 3 3/4 tsp. of baking powder.