According to the Marco's pizza chain, a 16-inch pizza yields 12 full slices. If one slice is considered a serving, then a 16 inch pizza feeds 12 people. The number of people this pizza feeds depends on the amount of pizza each person eats.
If each person eats two slices, then a large 16-inch pizza only feeds six people. It is possible to request that pizzerias halve the slices of their pizzas. This means that they make a couple of extra cuts to produce more slices in a pizza, making 24 half-slices in the case of a 12-slice pizza. This helps people stretch the pizza further.