What is the average size of a breakfast nook (in a 5 bedroom house)?
I don't think there's an average size to it. Take the size of your table, add to it about 35 inches on all sides, and this is the smallest size you can have if you want to be able to serve the food from behind a sitting person. If there's any other furniture in this space, you'd need to consider its dimensions too. As I said, this is the minimum size.