The number of meatballs needed for 100 people depends upon their size and the manner in which they are served. A standard main course serving size is 6 ounces of meat per guest, or approximately 600 1-ounce meatballs, 400 1 1/2-ounce meatballs, 300 2-ounce meatballs and 200 3-ounce meatballs.
To make sure that everyone is fed at a large dinner party or event, serve large, 3-ounce meatballs on their own. Pair medium-sized meatballs with pasta and plan for 1 1/2 to 2 ounces of pasta per guest. Soup can be served with small, 1/2-ounce meatballs. Less meat is needed when meatballs are served as an appetizer, typically 2 to 3 ounces or six bites per guest.