Self-rising flour is commonly called for in recipes for biscuits, pancakes and muffins. But if you don’t have room in your kitchen for multiple varieties of flour (or just don’t feel like going to the store) Epicurious has an easy formula for making your own with AP and a bit of salt and baking powder:
Add 1 1/2 teaspoons baking powder and 1/4 teaspoon salt to one cup of all-purpose flour
(For those who measure ingredients by mass, that would be: 6.9g baking powder and 1.42g of salt to 120g of all-purpose flour.)
One thing worth noting is that self-rising flour is milled from a lower-protein wheat than all-purpose, making for a more tender baked good. So though this substitution takes care of the “rising”, the resulting texture may be slightly tougher than what you’re aiming for. This isn’t necessarily a huge deal, but if you’re trying to make your famous “lighter than air biscuits”, it’s something to keep in mind.
Flour Hacks: Make Your Own Cake or Self-Rising Flour [Epicurious]