Reheat leftover pizza in the oven by placing a baking sheet into a cold oven and then setting the oven temperature to 400 Fahrenheit. Once the oven is preheated, place the pizza slices on the heated baking sheet, and bake them for approximately 10 minutes.
For larger or thicker slices with more toppings, add five minutes to the baking time. According to All American Johnny's Pizza Grill, pizza slices can also be placed on aluminum foil and baked at 325 F for 10 to 15 minutes. Toaster ovens can also be used to reheat pizza, although the cheese topping might not melt as evenly as it would in a conventional oven.