An average serving of wonton soup is about 8 ounces or 1 cup.  This means that if you are serving 4 people, you will need about 32 ounces, or 4 cups, of wonton soup.  You can also adjust the amount depending on how hungry your guests are and how hearty of a meal you want to serve.  For a lighter lunch or snack, one cup per person may suffice. For a heavier meal, two or more cups per person may be necessary.