Pizza Math: If you are ordering for a large party, plan on 2-3 slices per person. Most large pizzas are between 10-12 slices. If you are having a party of 20, you will need approximately 5 large pizzas. If you are hosting a kids' party, you can request the restaurant to double slice for younger kids. The most popular pizzas are pepperoni and plain cheese so keep that in mind when ordering.