To convert plain flour to self-rising flour, a person can combine 2 teaspoons of baking powder to every cup of the all-purpose flour. However, if one is using ingredients in a baking recipe, such as cocoa or buttermilk, then one can also add 1/4 teaspoon of baking soda with the baking powder for leavening purposes.
Before using the baking powder and all-purpose flour, one should sift these ingredients together in a bowl. This ensures that the ingredients are mixed thoroughly. Similarly, one should check the expiration date on the baking powder. An expired product will not allow baked goods to rise properly.
Alternatively, if one does not have baking powder, then one can use a slightly different method to convert all-purpose flour to self-rising flour. This method is to use 1/2 teaspoon of baking soda combined with 1 teaspoon of cream of tartar and add this to 1 cup of all-purpose flour to make 1 cup of self-rising flour.