Does anyone know approximately how many cups of batter will make 12 cupcakes?

it depends on how much batter you put in your cupcakes and what size cupcakes you're making.

I use a #20 scoop for my standard cupcakes which is about 3T. So i need 36 Tablespoons for one dozen which comes out to right about 2-1/4 cups of batter (plus a little more just becuase you don't always get everything out of the bowl.

HTH

How much batter depends on how big the cup is: how full you are going to fill it: and what cake recipe you are using:

Generally speaking -

Half cup size filled with minimum 1/3 cup batter x 12 = 4 cups batter total

Third cup size filled with minimum 1/4 cup batter x 12 = 3 cups batter total

Mini size [1 ounce] filled with minimum 1 tablespoon [4 teaspoons is better] x 24 = 1 1/2 cups batter batter total

Lots of times it is all personal choice, and what you think looks good for your cupcakes ..