What is the correct ratio to make self-rising flour?
For 1 cup self-raising flour, add 1½ tsp baking powder+ ¼ tsp salt to 1 cup all purpose flour. (http://www.joyofbaking.com/IngredientSubstitution.html)

Edit: Calculation added by Sebbidychef: 

According to http://www.jsward.com/cooking/conversion.shtml 1 cup of un-sifted all-purpose flour is equal to 120g.

Therefore 1000 divided by 120 is 8.3 recurring (1000/120=8.3).

8.3 multiplied by 1.5 (1 1/2 teaspoons) is 12.45 , so let's round it to 12.5 (12 1/2 teaspoons or 4.167 tablespoons, rounded to 4 tablespoons), (8.3*1.5=12.45). In metric this is 45g of baking powder.

8.3 multiplied by 0.25 is 2.075, so let's round it to 2 (2 teaspoons), (8.3*0.25=2.075). In metric this is 10g if salt.

So for 1kg of flour you will need 45g baking powder (4 tablespoons) of baking powder and 10g (2 teaspoons) of salt.