How much of cocoa powder would you need in a batch of cupcakes?

It all depends on the size of the batch you are making. Here is a basic chocolate cake recipe the can be used for cupcakes or regular cakes. 1 cup butter, 1 3/4 cup white sugar, 3 eggs, 1 1/2 teaspoon vanilla extract, 1 1/2 cup milk, 2 1/2 cups all purpose flour, 6 tablespoons unsweetened cocoa powder, 1 1/2 teaspoon baking soda, 1 teaspoon salt. Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan. Sift together the flour, cocoa, baking soda and salt. Set aside.In a large bowl, cream together the margarine and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Beat in the flour mixture alternately with the milk, mixing just until incorporated. Pour batter into prepared pan.Bake in the preheated oven for 40 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.You can double or triple a recipe for the size you need, but keep in mind that some recipes do not multiply well and you will just have to make multiple single batches.