How the estimate works
The calculator multiplies your guest count by the slices per person you choose to get the total slices needed. It then divides by the slices in your chosen pizza size and rounds up, since you cannot order a fraction of a pizza. The leftover figure shows how many slices you will have beyond what your guests need.
Tips for ordering
Mix a few toppings so there is something for everyone, and include at least one cheese or vegetarian option. If your party runs long or includes very hungry guests, bump up the appetite setting or add a pizza. Ordering a couple of larger pizzas is often cheaper per slice than many small ones.