What do I add to regular flour to make self rising flour

You will find out if you want to make biscuits and you need to use self-rising flour just by making the biscuits. If they rise it will be self-rising flour. That would be a good way to figure it our. Good Luck!

self rising flour uses baking powder as a leveling agent, so it rises as it is being heated in the cooking process, not like a yeast dough.
the following is taken from another site, I could not have said it any better.

Self-rising flour has an almost magical sound to it. And if you look at recipes that call for it, you'll see that they do not call for the addition of salt or leavening agents, though biscuits, cakes and breads made with seem to rise up just fine. The reason for this is that self-rising flour is actually nothing of the sort. It is flour that has a leavening agent - baking powder - and salt added to it during packaging. Since the ingredients are evenly distributed throughout the flour, you will get the same nice lift to your baked goods every time you use it. If you don't have self-rising flour and you have a recipe that calls for it, you can make your own by combining 1 cup all purpose flour with 1 tsp baking powder and 1/4 tsp salt. Similarly, if you only have self-rising flour, you can reduce the baking powder and salt called for in a recipe that uses standard all purpose flour.
Now that being said, it is also worth noting that there are several brands of self-rising flour that have a lower protein content than all purpose flour (11% protein). They are effectively cake flours (8% protein). Wheat protein, or gluten, is what gives baked goods much of their structure, but it can also cause a bread to be too dense or tough. White Lily and Presto are two examples of self-rising brands that use a low-protein cake flour as their base, and if a recipe calls for one of them, you should use cake flour in place of all purpose in the conversion given above.

Ingredients

Original recipe makes 1 cup

• 1 cup all-purpose flour
• 1/2 teaspoon salt

• 1 1/2 teaspoons baking powder

Directions

1. Stir or sift together the flour, salt, and baking powder. Presto, you've got self-rising flour!

For every cup of all-purpose flour you add 1 1/2 teaspoons baking powder and 1/2 teaspoon salt. Mix well.

For every cup of all-purpose flour you add 1 1/2 teaspoons baking powder and 1/2 teaspoon salt. Mix well.

For every cup of all-purpose flour add 1 1/2 teaspoons baking powder and 1/2 teaspoons salt. Mix well.

Add 1 1/2 teaspoons baking powder and 1/2 teaspoon salt to your 1 cup all-purpose flour and mix well.

For every cup of all-purpose flour add 1 1/2 teaspoons baking powder and 1/2 teaspoon salt and mix well.

For every cup of all-purpose flour add 1 1/2 teaspoons baking powder and 1/2 teaspoon salt and mix well.

1 cup of self rising flour is 1 cup minus 1 tablespoon of regular flour and 1.5 tsp baking powder and 1/8 tsp salt.