I am not good a measuring. It drives my daughter nuts. I just kind of make things up as I go. But this is close.
3/4 pkg of powdered sugar
1 pkg of fat free cream cheese.
1 tablespoon vanilla
milk around 3 table spoons start with 1 tablespoon and add as needed to get frosting spredable.
I am sorry I don't know the cals. I never worry about that just amount of fat serves 12 and fat count does count frosting.