What do you add to all purpose flour make it self raising flour?

To make self-raising flour, you'll need all purpose flour, baking powder, and salt. The general rule of thumb is to add 1 1/2 teaspoons of baking powder and 1/4 teaspoon of salt for every cup of all-purpose flour. Be sure to mix well to ensure that the baking powder and salt are evenly distributed throughout the flour.