How many people it serves depends on what part of the meal it's intended to serve. If it's served as an appetizer, serve about a cup per serving. If it's the main course, you'll want at least 2, possibly 3 cups per serving, depending on the other menu items that make up the meal - appetizer, salad, bread, dessert, etc.
Soup garnishes matter, too. Is the soup garnished with croutons? Cheese? Herbs? All the components of the recipe go into consideration, as do the rest of the items on your menu.